mac80211 has a reference to __bitmap_empty() via bitmap_empty().  In
lib/bitmap.c this is flagged with an EXPORT_SYMBOL(), but this is
ultimately ineffective due to bitmap.o being linked in lib-y, resulting in:

ERROR: "__bitmap_empty" [net/mac80211/mac80211.ko] undefined!

Moving bitmap.o to obj-y fixes this up.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>
Cc: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>