[GFS2] Given device ID rather than s_id in "id" sysfs file

This patch changes the /sys/fs/gfs2/<s_id>/id file to give the device
id "major:minor" rather than the s_id.  That enables gfs2_tool to
match devices properly (by id, not name) when locating the tuning files.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/sys.c

@@ -32,7 +32,8 @@ spinlock_t gfs2_sys_margs_lock;
 
 static ssize_t id_show(struct gfs2_sbd *sdp, char *buf)
 {
-	return snprintf(buf, PAGE_SIZE, "%s\n", sdp->sd_vfs->s_id);
+	return snprintf(buf, PAGE_SIZE, "%u:%u\n",
+			MAJOR(sdp->sd_vfs->s_dev), MINOR(sdp->sd_vfs->s_dev));
 }
 
 static ssize_t fsname_show(struct gfs2_sbd *sdp, char *buf)