microblaze: fix memory leak

When not assign a -dtb argument, the variable dtb_filename
storage returned from qemu_find_file(), which should be freed
after use. Alternatively we define a local variable filename,
with 'char *' type, free after use.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/microblaze/boot.c

@@ -113,15 +113,15 @@ void microblaze_load_kernel(MicroBlazeCPU *cpu, hwaddr ddr_base,
     const char *kernel_filename;
     const char *kernel_cmdline;
     const char *dtb_arg;
+    char *filename = NULL;
 
     machine_opts = qemu_get_machine_opts();
     kernel_filename = qemu_opt_get(machine_opts, "kernel");
     kernel_cmdline = qemu_opt_get(machine_opts, "append");
     dtb_arg = qemu_opt_get(machine_opts, "dtb");
-    if (dtb_arg) { /* Preference a -dtb argument */
-        dtb_filename = dtb_arg;
-    } else { /* default to pcbios dtb as passed by machine_init */
-        dtb_filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, dtb_filename);
+    /* default to pcbios dtb as passed by machine_init */
+    if (!dtb_arg) {
+        filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, dtb_filename);
     }
 
     boot_info.machine_cpu_reset = machine_cpu_reset;
@@ -203,7 +203,8 @@ void microblaze_load_kernel(MicroBlazeCPU *cpu, hwaddr ddr_base,
                             boot_info.initrd_start,
                             boot_info.initrd_end,
                             kernel_cmdline,
-                            dtb_filename);
+                            /* Preference a -dtb argument */
+                            dtb_arg ? dtb_arg : filename);
     }
-
+    g_free(filename);
 }