[XFS] shrink mrlock_t

The writer field is not needed for non_DEBU builds so remove it. While
we're at i also clean up the interface for is locked asserts to go through
and xfs_iget.c helper with an interface like the xfs_ilock routines to
isolated the XFS codebase from mrlock internals. That way we can kill
mrlock_t entirely once rw_semaphores grow an islocked facility. Also
remove unused flags to the ilock family of functions.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30902a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_utils.c b/fs/xfs/xfs_utils.c
index 2b8dc7e..27075c9 100644
--- a/fs/xfs/xfs_utils.c
+++ b/fs/xfs/xfs_utils.c
@@ -310,7 +310,7 @@
 {
 	xfs_mount_t	*mp;
 
-	ASSERT(ismrlocked (&ip->i_lock, MR_UPDATE));
+	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 	ASSERT(ip->i_d.di_version == XFS_DINODE_VERSION_1);
 
 	ip->i_d.di_version = XFS_DINODE_VERSION_2;