net: phy: micrel: fix shared interrupt on LAN8814

Since commit ece19502 ("net: phy: micrel: 1588 support for LAN8814
phy") the handler always returns IRQ_HANDLED, except in an error case.
Before that commit, the interrupt status register was checked and if
it was empty, IRQ_NONE was returned. Restore that behavior to play nice
with the interrupt line being shared with others.

Fixes: ece19502

 ("net: phy: micrel: 1588 support for LAN8814 phy")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Divya Koppera <Divya.Koppera@microchip.com>
Link: https://lore.kernel.org/r/20220920141619.808117-1-michael@walle.cc


Signed-off-by: Jakub Kicinski <kuba@kernel.org>