net: amd-xgbe: fix comparison to bitshift when dealing with a mask

Due to a typo, the mask was destroyed by a comparison instead of a bit
shift.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>