[XFS] kill XFS_ICSB_SB_LOCKED

With the last two patches XFS_ICSB_SB_LOCKED is never checked and only
superflously passed to xfs_icsb_count, so kill it.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30920a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>