include: audio: dmic: fixup parse_channel_map implementation

Fixup parse_channel_map implementation. The previous implementation of
this function did not use the "channel_map" values passed in by the
user, and would not return correct values for the PDM hardware
controller or L/R value. This function is not being used in tree, so
correcting the implementation to align with documentation should have
minimal affect.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>