hw/i386/pc: avoid an assignment in if condition in x86_load_linux()

Follow checkpatch.pl recommendation and avoid an assignment in if
condition in x86_load_linux().

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

hw/i386/pc.c

@@ -1045,7 +1045,14 @@ static void x86_load_linux(PCMachineState *pcms,
 
     /* load the kernel header */
     f = fopen(kernel_filename, "rb");
-    if (!f || !(kernel_size = get_file_size(f)) ||
+    if (!f) {
+        fprintf(stderr, "qemu: could not open kernel file '%s': %s\n",
+                kernel_filename, strerror(errno));
+        exit(1);
+    }
+
+    kernel_size = get_file_size(f);
+    if (!kernel_size ||
         fread(header, 1, MIN(ARRAY_SIZE(header), kernel_size), f) !=
         MIN(ARRAY_SIZE(header), kernel_size)) {
         fprintf(stderr, "qemu: could not load kernel '%s': %s\n",