Revert "Makefile: Do not quote value for CONFIG_CC_IMPLICIT_FALLTHROUGH"

This reverts commit cd8c917a.

Commit 129ab0d2 ("kbuild: do not quote string values in
include/config/auto.conf") provided the final solution.

Now reverting the temporary workaround.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -778,7 +778,7 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
 KBUILD_CFLAGS += $(stackp-flags-y)
 
 KBUILD_CFLAGS-$(CONFIG_WERROR) += -Werror
-KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH:"%"=%)
+KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
 
 ifdef CONFIG_CC_IS_CLANG
 KBUILD_CPPFLAGS += -Qunused-arguments