powerpc/boot: Makefile cleanup

The $(image-n) variable will never exist, because unset Kconfig options
are '' and not 'n'.
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/boot/Makefile

@@ -317,7 +317,7 @@ endif
 # Allow extra targets to be added to the defconfig
 image-y	+= $(subst ",,$(CONFIG_EXTRA_TARGETS))
 
-initrd-  := $(patsubst zImage%, zImage.initrd%, $(image-n) $(image-))
+initrd-  := $(patsubst zImage%, zImage.initrd%, $(image-))
 initrd-y := $(patsubst zImage%, zImage.initrd%, \
 		$(patsubst dtbImage%, dtbImage.initrd%, \
 		$(patsubst simpleImage%, simpleImage.initrd%, \