rt5645: re-enable headset mic functionality

The realtek ALC5645 data sheet is unclear about the state of the IN1 port
control mixer register, MX-0A, in that enabling bit 2 (En_bst1, also called "IN1
Port Enable Control") actually *prevents* the headset microphones from
functioning.

Change-Id: I560ac2e98301131dab4f70cf1a996553e61cefc0
1 file changed