[GFS2] Introduce gfs2_remove_from_ail

This collects together the operations required to remove a gfs2_bufdata
from the ail lists. Its only called from two places to start with, but
expect to see more of this function in future.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 7ef6b23..b17346a 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -60,11 +60,7 @@
 		blkno = bh->b_blocknr;
 		gfs2_assert_withdraw(sdp, !buffer_busy(bh));
 
-		bd->bd_ail = NULL;
-		list_del(&bd->bd_ail_st_list);
-		list_del(&bd->bd_ail_gl_list);
-		atomic_dec(&gl->gl_ail_count);
-		brelse(bh);
+		gfs2_remove_from_ail(NULL, bd);
 		gfs2_log_unlock(sdp);
 
 		gfs2_trans_add_revoke(sdp, blkno);