kbuild: remove UIMAGE_IN and UIMAGE_OUT

The only/last user of UIMAGE_IN/OUT was removed by commit 4722a3e6
("microblaze: fix multiple bugs in arch/microblaze/boot/Makefile").

The input and output should always be $< and $@.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.lib

@@ -371,15 +371,13 @@ UIMAGE_TYPE ?= kernel
 UIMAGE_LOADADDR ?= arch_must_set_this
 UIMAGE_ENTRYADDR ?= $(UIMAGE_LOADADDR)
 UIMAGE_NAME ?= 'Linux-$(KERNELRELEASE)'
-UIMAGE_IN ?= $<
-UIMAGE_OUT ?= $@
 
-quiet_cmd_uimage = UIMAGE  $(UIMAGE_OUT)
+quiet_cmd_uimage = UIMAGE  $@
       cmd_uimage = $(CONFIG_SHELL) $(MKIMAGE) -A $(UIMAGE_ARCH) -O linux \
 			-C $(UIMAGE_COMPRESSION) $(UIMAGE_OPTS-y) \
 			-T $(UIMAGE_TYPE) \
 			-a $(UIMAGE_LOADADDR) -e $(UIMAGE_ENTRYADDR) \
-			-n $(UIMAGE_NAME) -d $(UIMAGE_IN) $(UIMAGE_OUT)
+			-n $(UIMAGE_NAME) -d $< $@
 
 # XZ
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