s390/decompressor: avoid constant startup.a rebuilds

Correct merging error which replaced startup.a in targets list with
non-existing setup.a. Due to missing startup.a in targets list if_changed
triggered startup.a rebuild unconditionally.

Fixes: 3e200c54438d ("s390/decompressor: avoid reusing uncompressed image objects")
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/boot/Makefile

@@ -28,7 +28,7 @@ endif
 CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char
 
 obj-y	:= head.o als.o ebcdic.o sclp_early_core.o mem.o
-targets	:= bzImage setup.a $(obj-y)
+targets	:= bzImage startup.a $(obj-y)
 subdir-	:= compressed
 
 OBJECTS := $(addprefix $(obj)/,$(obj-y))