of_genpd_add_provider_simple() might fail, this patch makes sure we check
the return value of of_genpd_add_provider_simple() by propagating the
return value to the caller of rzg2l_cpg_add_clk_domain().

Fixes: ef3c613c ("clk: renesas: Add CPG core wrapper for RZ/G2L SoC")
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20211117115101.28281-3-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>