net: dsa: vsc73xxx: Make vsc73xx_remove() return void

vsc73xx_remove() returns zero unconditionally and no caller checks the
returned value. So convert the function to return no value.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>