brcm47xx: image: use standard KERNEL_IMAGE to avoid warnings

KERNEL_IMAGE is used as target rule so reusing the same name causes:
Makefile:326: warning: overriding recipe for target `bin/brcm47xx/vmlinux.lzma'
Makefile:326: warning: ignoring old recipe for target `bin/brcm47xx/vmlinux.lzma'
Makefile:326: warning: overriding recipe for target `build_dir/target-mipsel_74kc+dsp2_uClibc-0.9.33.2/linux-brcm47xx_mips74k/vmlinux.lzma'
Makefile:326: warning: ignoring old recipe for target `build_dir/target-mipsel_74kc+dsp2_uClibc-0.9.33.2/linux-brcm47xx_mips74k/vmlinux.lzma'

Unfortunately this will cause copying vmlinux.lzma over and over like:
cp vmlinux.lzma FOO-kernel.bin
which is redundant on brcm47xx where we never modify kernel image.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

SVN-Revision: 45178

target/linux/brcm47xx/image/Makefile

@@ -138,8 +138,9 @@ DEVICE_VARS += DEVICE_ID VERSION
 DEVICE_VARS += BOARD_ID REGION
 
 define Device/Default
+	KERNEL := kernel-bin
 	IMAGE_NAME = $$(IMAGE_PREFIX)-$$(1).$$(2)
-	KERNEL_IMAGE = vmlinux.lzma
+	KERNEL_NAME = vmlinux.lzma
 	FILESYSTEMS := $(FS_64K)
 	IMAGES := trx
 	IMAGE/trx := trx-with-loader