clk: msm: clock-alpha-pll: Wait for the FSM to turn off the PLL

It is necessary to check that a PLL is completely disabled
before invoking code that would modify PLL configuration.
For FSM controlled PLLs, check the PLL active flag before
exiting the function since we may be in a set_rate op on
the PLL.

This is really not necessary for other FSM controlled PLLs
that have a fixed rate.

Change-Id: I6b0e4e6a0ccfa7949a1996fb8911e1f7044d725a
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>