net: systemport: Fix an error handling path in bcm_sysport_probe()

if devm_clk_get_optional() fails, we still need to go through the error
handling path.

Add the missing goto.

Fixes: 6328a126 ("net: systemport: Manage Wake-on-LAN clock")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/99d70634a81c229885ae9e4ee69b2035749f7edc.1652634040.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Paolo Abeni <pabeni@redhat.com>