net/mlx5: remove unreachable return

The last return statement is unreachable code. I'm not sure if it will
provoke any warnings, but it looks ugly.
Signed-off-by: Pavel Machek (CIP) <pavel@denx.de>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c

@@ -435,8 +435,6 @@ static int mlx5_ptp_verify(struct ptp_clock_info *ptp, unsigned int pin,
 	default:
 		return -EOPNOTSUPP;
 	}
-
-	return -EOPNOTSUPP;
 }
 
 static const struct ptp_clock_info mlx5_ptp_clock_info = {