ASoC: pcm1789: Make pcm1789_common_exit() return void

ASoC: pcm1789: Make pcm1789_common_exit() return void

This function returns zero unconditionally, so there isn't any benefit
of returning a value. Make it return void to be able to see at a glance
that the return value of pcm1789_i2c_remove() is always zero.

This patch is a preparation for making i2c remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220425193023.61046-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>