ext4: rename: move EMLINK check up

Move checking i_nlink from after ext4_get_first_dir_block() to before.  The
check doesn't rely on the result of that function and the function only
fails on fs corruption, so the order shouldn't matter.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>