msm: acpuclock-8960: Skip HFPLL regulator during PLL reprogramming

When briefly disabling HFPLLs to reprogram their rates, there is
no need to de-assert and re-assert requests for the PLL's power rails.
Skip these the regulator enable/disable steps to save potential latency
waiting for the regulator calls to return.

Change-Id: I1f00b00123178a27655fd0d70834ac809149e694
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>