net: macb: Fix GEM hardware detection

Fix MID bit field check to correctly identify all GEM hardwares.

The check is updated as per macb driver in Linux location:
<linux_sources>/drivers/net/ethernet/cadence/macb_main.c:259

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>