clk: renesas: rzg2l: Avoid mixing error pointers and NULL

These functions accidentally return both error pointers and NULL when
there is an error.  It doesn't cause a problem but it is confusing and
seems unintentional.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/YMtY7nOtqEvTokh7@mwanda


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>