powerpc/boot: add simpleImage.* to clean-files list

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index 4458abb..bff7f12 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -367,7 +367,7 @@
 clean-files += $(image-) $(initrd-) cuImage.* dtbImage.* treeImage.* \
 	zImage zImage.initrd zImage.chrp zImage.coff zImage.holly \
 	zImage.iseries zImage.miboot zImage.pmac zImage.pseries \
-	otheros.bld *.dtb
+	simpleImage.* otheros.bld *.dtb
 
 # clean up files cached by wrapper
 clean-kernel := vmlinux.strip vmlinux.bin