net: phy: dp83867: Disable IRQs on suspend

Before putting the PHY into IEEE power down mode, disable IRQs to
prevent accessing the PHY once MDIO has already been shutdown.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230310074500.3472858-1-alexander.stein@ew.tq-group.com


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