ARM: dts: Correct audio input route & set mic bias for am335x-pepper

Audio-in was incorrectly routed to Line In. It should be Mic3L as per
schematic.

Using mic-bias voltage at 2.0v (<0x1>) does not work for some reason. There
is no voltage seen on micbias (R127). Mic-bias voltage of 2.5v (<0x2>) works.
I see voltage of 2.475v across GND and micbias.

With these changes, I can record audio with a pair of proliferate TRRS earbuds.

Signed-off-by: Adam YH Lee <adam.yh.lee@gmail.com>
Acked-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>