firmware: arm_scmi: Harden clock parents discovery

firmware: arm_scmi: Harden clock parents discovery

Fix clock parents enumeration to account only for effectively discovered
parents during enumeration, avoiding to trust the total number of parents
declared upfront by the platform.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260508153300.2224715-9-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>