io_uring: use kvfree() in io_sqe_buffer_register()

Use kvfree() to free the pages and vmas, since they are allocated by
kvmalloc_array() in a loop.

Fixes: d4ef647510 ("io_uring: avoid page allocation warnings")
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200605093203.40087-1-efremov@linux.com

fs/io_uring.c

@@ -7171,8 +7171,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 
 		ret = 0;
 		if (!pages || nr_pages > got_pages) {
-			kfree(vmas);
-			kfree(pages);
+			kvfree(vmas);
+			kvfree(pages);
 			pages = kvmalloc_array(nr_pages, sizeof(struct page *),
 						GFP_KERNEL);
 			vmas = kvmalloc_array(nr_pages,