net: stmmac: Make stmmac_dvr_remove() return void

net: stmmac: Make stmmac_dvr_remove() return void

The function returns zero unconditionally. Change it to return void instead
which simplifies some callers as error handing becomes unnecessary.

This also makes it more obvious that most platform remove callbacks always
return zero.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230211112431.214252-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>