btrfs: tree-checker: use %zu format string for size_t

We now get a harmless compile-time on 32-bit architectures:

fs/btrfs/tree-checker.c: In function 'check_extent_data_item':
fs/btrfs/tree-checker.c:189:70: error: format '%lu' expects argument of type 'long unsigned int', but argument 6 has type 'unsigned int' [-Werror=format=]

This changes the format string to use %zu instead of %lu for size_t.

Fixes: c1f6520bf360 ("btrfs: tree-checker: Enhance output for check_extent_data_item")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-checker.c

@@ -182,7 +182,7 @@ static int check_extent_data_item(struct btrfs_root *root,
 	/* Regular or preallocated extent has fixed item size */
 	if (item_size != sizeof(*fi)) {
 		file_extent_err(root, leaf, slot,
-	"invalid item size for reg/prealloc file extent, have %u expect %lu",
+	"invalid item size for reg/prealloc file extent, have %u expect %zu",
 			item_size, sizeof(*fi));
 		return -EUCLEAN;
 	}