afs: Unlock pages for __pagevec_release()

__pagevec_release() complains loudly if any page in the vector is still
locked.  The pages need to be locked for generic_error_remove_page(), but
that function doesn't actually unlock them.

Unlock the pages afterwards.
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Jonathan Billings <jsbillin@umich.edu>

fs/afs/write.c

@@ -264,6 +264,7 @@ static void afs_kill_pages(struct address_space *mapping,
 				first = page->index + 1;
 			lock_page(page);
 			generic_error_remove_page(mapping, page);
+			unlock_page(page);
 		}
 
 		__pagevec_release(&pv);