bnx2: Fix register test on 5709.

The register BNX2_CTX_STATUS (0x1004) should be skipped on 5709 as it
contains reserved bits.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>