fw_cfg: fix FW_CFG_BOOT_DEVICE update on ppc and sparc

On ppc, sparc, and sparc64, the value of the FW_CFG_BOOT_DEVICE 16bit
fw_cfg entry is repeatedly modified from a series of callbacks, which
currently results in the previous value's dynamically allocated memory
being leaked.

This patch switches updating to the new fw_cfg_modify_i16() call, which
does not cause memory leaks.
Signed-off-by: NGabriel Somlo <somlo@cmu.edu>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/ppc/mac_newworld.c

@@ -119,7 +119,7 @@ static const MemoryRegionOps unin_ops = {
 static void fw_cfg_boot_set(void *opaque, const char *boot_device,
                             Error **errp)
 {
-    fw_cfg_add_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
+    fw_cfg_modify_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
 }
 
 static uint64_t translate_kernel_address(void *opaque, uint64_t addr)

hw/ppc/mac_oldworld.c

@@ -52,7 +52,7 @@
 static void fw_cfg_boot_set(void *opaque, const char *boot_device,
                             Error **errp)
 {
-    fw_cfg_add_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
+    fw_cfg_modify_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
 }
 
 static uint64_t translate_kernel_address(void *opaque, uint64_t addr)

hw/sparc/sun4m.c

@@ -124,7 +124,7 @@ void DMA_register_channel (int nchan,
 static void fw_cfg_boot_set(void *opaque, const char *boot_device,
                             Error **errp)
 {
-    fw_cfg_add_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
+    fw_cfg_modify_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
 }
 
 static void nvram_init(Nvram *nvram, uint8_t *macaddr,

hw/sparc64/sun4u.c

@@ -127,7 +127,7 @@ void DMA_register_channel (int nchan,
 static void fw_cfg_boot_set(void *opaque, const char *boot_device,
                             Error **errp)
 {
-    fw_cfg_add_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
+    fw_cfg_modify_i16(opaque, FW_CFG_BOOT_DEVICE, boot_device[0]);
 }
 
 static int sun4u_NVRAM_set_params(Nvram *nvram, uint16_t NVRAM_size,