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

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

This reverts commit 50a7fa23e4b36ea6312641faf6524945f5ff726a.
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>