net: stmmac: Rename phylink_get_caps() callback to update_caps()

Since recent commits the stmmac_ops::phylink_get_caps() callback has no
longer been responsible for the phylink MAC capabilities getting, but
merely updates the MAC capabilities in the mac_device_info::link::caps
field. Rename the callback to comply with the what the method does now.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Romain Gantois <romain.gantois@bootlin.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>