s390x: fix flat file load on 32 bit systems

pc-bios/s390-zipl.rom is a flat image so it's expected that
loading it as elf will fail.
It should fall back on loading a flat file, but doesn't
on 32 bit systems, instead it fails printing:
    qemu: hardware error: could not load bootloader 's390-zipl.rom'

The result is boot failure.

The reason is that a 64 bit unsigned interger which is set
to -1 on error is compared to -1UL which on a 32 bit system
with gcc is a 32 bit unsigned interger.
Since both are unsigned, no sign extension takes place and
comparison evaluates to non-equal.

There's no reason to do clever tricks: all functions
we call actually return int so just use int.
And then we can use == -1 everywhere, consistently.

Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/s390x/ipl.c

@@ -62,10 +62,10 @@ typedef struct S390IPLState {
 static int s390_ipl_init(SysBusDevice *dev)
 {
     S390IPLState *ipl = S390_IPL(dev);
-    ram_addr_t kernel_size = 0;
+    int kernel_size;
 
     if (!ipl->kernel) {
-        ram_addr_t bios_size = 0;
+        int bios_size;
         char *bios_filename;
 
         /* Load zipl bootloader */
@@ -80,7 +80,7 @@ static int s390_ipl_init(SysBusDevice *dev)
 
         bios_size = load_elf(bios_filename, NULL, NULL, &ipl->start_addr, NULL,
                              NULL, 1, ELF_MACHINE, 0);
-        if (bios_size == -1UL) {
+        if (bios_size == -1) {
             bios_size = load_image_targphys(bios_filename, ZIPL_IMAGE_START,
                                             4096);
             ipl->start_addr = ZIPL_IMAGE_START;
@@ -90,17 +90,17 @@ static int s390_ipl_init(SysBusDevice *dev)
         }
         g_free(bios_filename);
 
-        if ((long)bios_size < 0) {
+        if (bios_size == -1) {
             hw_error("could not load bootloader '%s'\n", bios_name);
         }
         return 0;
     } else {
         kernel_size = load_elf(ipl->kernel, NULL, NULL, NULL, NULL,
                                NULL, 1, ELF_MACHINE, 0);
-        if (kernel_size == -1UL) {
+        if (kernel_size == -1) {
             kernel_size = load_image_targphys(ipl->kernel, 0, ram_size);
         }
-        if (kernel_size == -1UL) {
+        if (kernel_size == -1) {
             fprintf(stderr, "could not load kernel '%s'\n", ipl->kernel);
             return -1;
         }
@@ -115,15 +115,16 @@ static int s390_ipl_init(SysBusDevice *dev)
         ipl->start_addr = KERN_IMAGE_START;
     }
     if (ipl->initrd) {
-        ram_addr_t initrd_offset, initrd_size;
+        ram_addr_t initrd_offset;
+        int initrd_size;
 
         initrd_offset = INITRD_START;
         while (kernel_size + 0x100000 > initrd_offset) {
             initrd_offset += 0x100000;
         }
         initrd_size = load_image_targphys(ipl->initrd, initrd_offset,
                                           ram_size - initrd_offset);
-        if (initrd_size == -1UL) {
+        if (initrd_size == -1) {
             fprintf(stderr, "qemu: could not load initrd '%s'\n", ipl->initrd);
             exit(1);
         }