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)/".

Change-Id: I2b2a83f2e389425e0ec1c6389391cf48509b0fc7
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>
Git-commit: 371cfd4ff0611d8bc5d18bbb9cc6a2bc3d56cd3d
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git


Signed-off-by: Mohammed Khajapasha <mkhaja@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>