afs: add missing up_write() on return

If afs_cell_alloc() fails, afs_cells_sem doesn't get unlocked, which
leads to a deadlock.  Unlock it before returning.
Signed-off-by: NSven Schnelle <svens@stackframe.org>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/afs/cell.c

@@ -138,6 +138,7 @@ struct afs_cell *afs_cell_create(const char *name, char *vllist)
 	cell = afs_cell_alloc(name, vllist);
 	if (IS_ERR(cell)) {
 		_leave(" = %ld", PTR_ERR(cell));
+		up_write(&afs_cells_sem);
 		return cell;
 	}