net: mvmdio: fix compilation warning

net: mvmdio: fix compilation warning

The kernel test robot reported a following issue:

>> drivers/net/ethernet/marvell/mvmdio.c:426:36: warning:
unused variable 'orion_mdio_acpi_match' [-Wunused-const-variable]
   static const struct acpi_device_id orion_mdio_acpi_match[] = {
                                      ^
   1 warning generated.

Fix that by surrounding the variable by appropriate ifdef.

Fixes: c54da4c1acb1 ("net: mvmdio: add ACPI support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20211115153024.209083-1-mw@semihalf.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>