lib: Remove trailing whitespaces

Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/lib/priority_queue.c

@@ -139,7 +139,7 @@ void
 grub_priority_queue_pop (grub_priority_queue_t pq)
 {
   grub_size_t p;
-  
+
   swap (pq, 0, pq->used - 1);
   pq->used--;
   for (p = 0; left_child (p) < pq->used; )