kbuild: mergeconfig: remove redundant $(objtree)

Kbuild always runs in $(objtree).  Actually, $(objtree) is always
set to "." by the top-level Makefile.

We can omit "-O $(objtree)" and "$(objtree)/".
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/Makefile

@@ -108,7 +108,7 @@ configfiles=$(wildcard $(srctree)/kernel/configs/$(1).config $(srctree)/arch/$(S
 
 define mergeconfig
 $(if $(call configfiles,$(1)),, $(error No configuration exists for this target on this architecture))
-$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh -m -O $(objtree) $(objtree)/.config $(call configfiles,$(1))
+$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh -m .config $(call configfiles,$(1))
 +$(Q)yes "" | $(MAKE) -f $(srctree)/Makefile oldconfig
 endef