aio: remove incorrect initialization of "nr_pages"

We should not claim to have filled in the ring_pages[] array
until we actually _do_ fill it in. It will confuse the code
that frees the structure if we claim there are pages there
that don't exist.

Noted by Darrick Wong.

fs/aio.c

@@ -118,8 +118,6 @@ static int aio_setup_ring(struct kioctx *ctx)
 	if (nr_pages < 0)
 		return -EINVAL;
 
-	info->nr_pages = nr_pages;
-
 	nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring)) / sizeof(struct io_event);
 
 	info->nr = 0;