ext4l: Export ext4_readdir() for directory listing

Remove the static qualifier from ext4_readdir() so it can be called
from the ext4l interface code for directory listing operations.

Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

fs/ext4l/dir.c

@@ -122,7 +122,7 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
 	return 1;
 }
 
-static int ext4_readdir(struct file *file, struct dir_context *ctx)
+int ext4_readdir(struct file *file, struct dir_context *ctx)
 {
 	unsigned int offset;
 	int i;