hal: Ensure during voice call backend in sample rate is fixed at 48kHz

-True native playback uses same backend to play 44.1kHz as well as
48kHz.
-During voice call if backend gets reconfigured to sample rate of
44.1kHz then voice call fails.
-Hence ensure that if voice call is active the backend irrespective
of native playback is fixed at sample rate of 48Khz.

Change-Id: I610d701bd89ae25acdd8cea63d03d77e9f791af6