ext4: Use generic_ci_validate_strict_name helper

Use the helper function to check the requirements for casefold
directories using strict encoding.

Suggested-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20241021-tonyk-tmpfs-v8-2-f443d5814194@igalia.com


Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>