squashfs: fix filename in header comment

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

fs/squashfs/xattr.c

@@ -18,7 +18,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  *
- * xattr_id.c
+ * xattr.c
  */
 
 #include <linux/init.h>