s390/mm: add __releases()/__acquires() annotations to gmap_alloc_table()

Let sparse not incorrectly complain about unbalanced locking.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -246,6 +246,8 @@ EXPORT_SYMBOL_GPL(gmap_disable);
  */
 static int gmap_alloc_table(struct gmap *gmap,
 			    unsigned long *table, unsigned long init)
+	__releases(&gmap->mm->page_table_lock)
+	__acquires(&gmap->mm->page_table_lock)
 {
 	struct page *page;
 	unsigned long *new;