net: phy: aquantia: do not return an error on clearing pending IRQs

The referenced commit added in .config_intr() the part of code which upon
configuration of the IRQ state it also clears up any pending IRQ. If
there were actually pending IRQs, a read on the IRQ status register will
return something non zero. This should not result in the callback
returning an error.

Fix this by returning an error only when the result of the
phy_read_mmd() is negative.

Fixes: e11ef96d ("net: phy: aquantia: remove the use of .ack_interrupt()")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Tested-by: Camelia Groza <camelia.groza@nxp.com>
Link: https://lore.kernel.org/r/20201109154601.3812574-1-ciorneiioana@gmail.com


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