xfs: Define a new function xfs_is_quota_inode()

In preparation for combined pquota/gquota support, define
a new function to check if the given inode is a quota inode.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_trans_dquot.c b/fs/xfs/xfs_trans_dquot.c
index fec75d0..3fa369c 100644
--- a/fs/xfs/xfs_trans_dquot.c
+++ b/fs/xfs/xfs_trans_dquot.c
@@ -157,8 +157,7 @@
 
 	if (!XFS_IS_QUOTA_RUNNING(mp) ||
 	    !XFS_IS_QUOTA_ON(mp) ||
-	    ip->i_ino == mp->m_sb.sb_uquotino ||
-	    ip->i_ino == mp->m_sb.sb_gquotino)
+	    xfs_is_quota_inode(&mp->m_sb, ip->i_ino))
 		return;
 
 	if (tp->t_dqinfo == NULL)
@@ -816,8 +815,7 @@
 	if (XFS_IS_PQUOTA_ON(mp))
 		flags |= XFS_QMOPT_ENOSPC;
 
-	ASSERT(ip->i_ino != mp->m_sb.sb_uquotino);
-	ASSERT(ip->i_ino != mp->m_sb.sb_gquotino);
+	ASSERT(!xfs_is_quota_inode(&mp->m_sb, ip->i_ino));
 
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 	ASSERT((flags & ~(XFS_QMOPT_FORCE_RES | XFS_QMOPT_ENOSPC)) ==