btrfs: fix kvcalloc() arguments order in btrfs_ioctl_send()

When compiling with gcc version 14.0.0 20231220 (experimental)
and W=1, I've noticed the following warning:

fs/btrfs/send.c: In function 'btrfs_ioctl_send':
fs/btrfs/send.c:8208:44: warning: 'kvcalloc' sizes specified with 'sizeof'
in the earlier argument and not in the later argument [-Wcalloc-transposed-args]
 8208 |         sctx->clone_roots = kvcalloc(sizeof(*sctx->clone_roots),
      |                                            ^

Since 'n' and 'size' arguments of 'kvcalloc()' are multiplied to
calculate the final size, their actual order doesn't affect the result
and so this is not a bug. But it's still worth to fix it.
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/send.c

@@ -8205,8 +8205,8 @@ long btrfs_ioctl_send(struct inode *inode, struct btrfs_ioctl_send_args *arg)
 		goto out;
 	}
 
-	sctx->clone_roots = kvcalloc(sizeof(*sctx->clone_roots),
-				     arg->clone_sources_count + 1,
+	sctx->clone_roots = kvcalloc(arg->clone_sources_count + 1,
+				     sizeof(*sctx->clone_roots),
 				     GFP_KERNEL);
 	if (!sctx->clone_roots) {
 		ret = -ENOMEM;