net: stmmac: dwmac-visconti: Make visconti_eth_clock_remove() return void

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

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>