net: macb: use NAPI_POLL_WEIGHT

Use NAPI_POLL_WEIGHT, the default NAPI poll() weight instead of
redefining our own value (which turns out to be 64 as well).

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>