be2net: fix wrong usage of adapter->generation

adapter->generation was being incorrectly set as BE_GEN3 for Skyhawk-R.
Replace generation usage with XXX_chip() macros to identify the chip.

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