greybus: audio: remove the unnecessary return statement

The return statement immediately after the BUG_ON of the gbcodec_write()
call is added by mistake. It's not causing any errors right now due to
that gbcodec_reg is currently not being used.

Testing Done:
- Audio playback on EVT2

Signed-off-by: David Lin <dtwlin@google.com>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>