[XFS] Kill off xfs_count_bits

xfs_count_bits is only called once, and is then compared to 0. IOW, what
it really wants to know is, is the bitmap empty. This can be done more
simply, certainly.

SGI-PV: 966503
SGI-Modid: xfs-linux-melb:xfs-kern:28944a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>