drivers/block/aoe/Makefile: replace the use of <module>-objs with <module>-y

Change Makefile to use <modules>-y instead of <modules>-objs because -objs
is deprecated and should now be switched.  According to
(documentation/kbuild/makefiles.txt).

Signed-off-by: Tracey Dent <tdent48227@gmail.com>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>