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

drivers/clk/renesas/renesas-rzg2l-cpg.c

@@ -125,7 +125,7 @@ rzg2l_cpg_div_clk_register(const struct cpg_core_clk *core,
 						 core->flag, &priv->rmw_lock);
 
 	if (IS_ERR(clk_hw))
-		return NULL;
+		return ERR_CAST(clk_hw);
 
 	return clk_hw->clk;
 }