net: phy: mscc: use phy_trigger_machine() to notify link change

According to the comment describing the phy_mac_interrupt() function, it
it intended to be used by MAC drivers which have noticed a link change
thus its use in the mscc PHY driver is improper and, most probably, was
added just because phy_trigger_machine() was not exported.
Now that we have acces to trigger the link state machine, use directly
the phy_trigger_machine() function to notify a link change detected by
the PHY driver.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>