readdir: Add missing quote in macro comment

Add a missing double quote in the unsafe_copy_dirent_name() macro
comment.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240602004729.229634-2-thorsten.blum@toblux.com


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>