Merge branch 'net-mvmdio-avoid-error-message-for-optional-IRQ'

Chris Packham says:

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net: mvmdio: avoid error message for optional IRQ

I've gone ahead an sent a revert. This is the same as the original v1 except
I've added Andrew's review to the commit message.
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Signed-off-by: David S. Miller <davem@davemloft.net>