net: ks8851: Make ks8851_remove_common() return void

Up to now ks8851_remove_common() returns zero unconditionally. Make it
return void instead which makes it easier to see in the callers that
there is no error to handle.

Also the return value of platform and spi remove callbacks is ignored
anyway.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>