Makefile: Initialize LIBDIR var correctly

BUG=chromium-os:38724
TEST=built and installed on link. Lib ended up in /usr/lib64 and
filter worked.

Change-Id: Ib6b942fe32979e28075dce19b586d353af8448db
Reviewed-on: https://gerrit.chromium.org/gerrit/42867
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Andrew de los Reyes <adlr@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
1 file changed