net: bgmac: remove a copy of the NAPI_POLL_WEIGHT define

Defining local versions of NAPI_POLL_WEIGHT with the same
values in the drivers just makes refactoring harder.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>