net: mvmdio: fix interrupt disable in remove path

net: mvmdio: fix interrupt disable in remove path

The pre-existing write to disable interrupts on the remove path happens
whether we have an interrupt or not.  While this may seem to be a good
idea, this driver is re-used in many different implementations, some
where the binding only specifies four bytes of register space.  This
access causes us to access registers outside of the binding.

Make it conditional on the interrupt being present, which is the same
condition used when enabling the interrupt in the first place.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>