XFS: fix xmount command in xfsidbg.

Modid: 2.5.x-xfs:slinx:128998a

fs/xfs/xfsidbg.c

@@ -4438,9 +4438,9 @@ xfsidbg_xmount(xfs_mount_t *mp)
 		mp->m_ail_gen, &mp->m_sb);
 	kdb_printf("sb_lock 0x%p sb_bp 0x%p dev 0x%x logdev 0x%x rtdev 0x%x\n",
 		&mp->m_sb_lock, mp->m_sb_bp,
-		mp->m_ddev_targp->pbr_dev,
-		mp->m_logdev_targp->pbr_dev,
-		mp->m_rtdev_targp->pbr_dev);
+		mp->m_ddev_targp ? mp->m_ddev_targp->pbr_dev : 0,
+		mp->m_logdev_targp ? mp->m_logdev_targp->pbr_dev : 0,
+		mp->m_rtdev_targp ? mp->m_rtdev_targp->pbr_dev : 0);
 	kdb_printf("bsize %d agfrotor %d agirotor %d ihash 0x%p ihsize %d\n",
 		mp->m_bsize, mp->m_agfrotor, mp->m_agirotor,
 		mp->m_ihash, mp->m_ihsize);