staging: greybus: audio_codec.c: code indent should use tabs where possible

Minor error spotted by checkpatch.pl in greybus
code indent should use tabs where possible
Signed-off-by: Richard Groux <rgroux@sauron-mordor.net>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>