Revert "net: mvmdio: avoid error message for optional IRQ"

Revert "net: mvmdio: avoid error message for optional IRQ"

This reverts commit e1f550dc44a4d535da4e25ada1b0eaf8f3417929.
platform_get_irq_optional() will still return -ENXIO when no interrupt
is provided so the additional error handling caused the driver prone to
fail when no interrupt was specified. Revert the change so we can apply
the correct minimal fix.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>