Makefile: fix HAVE_VENDOR_COMMON_LIB

Commit 8b5a0264 ("Makefile: cosmetic:
optimize usage of LIBS-y") broke the build of boards that have a board
vendor "common" directory, by introducing a space between "LIBS-" and
"y".

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Acked-by: Kim Phillips <kim.phillips@freescale.com>