[XFS] optimize XFS_IS_REALTIME_INODE w/o realtime config

Use XFS_IS_REALTIME_INODE in more places, and #define it to 0 if
CONFIG_XFS_RT is off. This should be safe because mount checks in
xfs_rtmount_init:

so if we get mounted w/o CONFIG_XFS_RT, no realtime inodes should be
encountered after that.

Defining XFS_IS_REALTIME_INODE to 0 saves a bit of stack space,
presumeably gcc can optimize around the various "if (0)" type checks:

xfs_alloc_file_space -8 xfs_bmap_adjacent -16 xfs_bmapi -8
xfs_bmap_rtalloc -16 xfs_bunmapi -28 xfs_free_file_space -64 xfs_imap +8
<-- ? hmm. xfs_iomap_write_direct -12 xfs_qm_dqusage_adjust -4
xfs_qm_vop_chown_reserve -4

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30014a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_bmap_btree.c b/fs/xfs/xfs_bmap_btree.c
index 32b49ec..c4181d8 100644
--- a/fs/xfs/xfs_bmap_btree.c
+++ b/fs/xfs/xfs_bmap_btree.c
@@ -2062,8 +2062,7 @@
 				pcur->bc_private.b.allocated;
 			pcur->bc_private.b.allocated = 0;
 			ASSERT((cur->bc_private.b.firstblock != NULLFSBLOCK) ||
-			       (cur->bc_private.b.ip->i_d.di_flags &
-				XFS_DIFLAG_REALTIME));
+			       XFS_IS_REALTIME_INODE(cur->bc_private.b.ip));
 			cur->bc_private.b.firstblock =
 				pcur->bc_private.b.firstblock;
 			ASSERT(cur->bc_private.b.flist ==