clk: clock-local2: Add set rate ops for gate clock

In some use cases, clients want to do clk_set_rate using
the gate clock. Therefore, support this case by passing
the set rate request to the parent clock.

Change-Id: Ic40e73b3fee04e841ed8f82516b34291408152e8
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>