be2net: use "if (!foo)" test style

Replace "if (foo == NULL)" statements with "if (!foo)" to be consistent
across the driver.

Signed-off-by: Kalesh AP <kalesh.purayil@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>