soc: imx: gpc: fix domain_index sanity check issue

ARRAY_SIZE(imx_gpc_domains) represents all power domains supported
by different SoCs. Driver should use SoC specific of_id_data->num_domains
instead to do power domain index sanity check.
e.g. MX6Q supports two power domains while MX6SL supports three.

Fixes: 721cabf6 ("soc: imx: move PGC handling to a new GPC driver")
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>