xtensa: remove meaningless export ccflags-y

arch/xtensa/boot/Makefile does not define ccflags-y at all.

Please do not export ccflags-y because it is meant to be effective
only in the current Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Message-Id: <20200310045925.25396-1-masahiroy@kernel.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/boot/Makefile

@@ -14,7 +14,6 @@ HOSTFLAGS	+= -Iarch/$(ARCH)/boot/include
 
 BIG_ENDIAN	:= $(shell echo __XTENSA_EB__ | $(CC) -E - | grep -v "\#")
 
-export ccflags-y
 export BIG_ENDIAN
 
 subdir-y	:= lib