fix(scmi): add parameter for plat_scmi_clock_rates_array

Pass "start_idx" to plat_scmi_clock_rates_array.
This parameter is required to obtain the rate table
a second time.

Signed-off-by: XiaoDong Huang <derrick.huang@rock-chips.com>
Change-Id: I97c6751e7d34c839ced8f22bddc39fb534978cc4