[SCSI] bnx2fc: Map the doorbell register between offload and enable requests

We used to map doorbell register after FW enable request is complete.
This causes a race condition when unsolicited event is received, and FW
sends a CQE for it. Since the doorbell is not mapped, driver does not
arm CQ, which means FW will not notify the driver for further CQ
completions.  To resolve this, map the doorbell between offload and
enable, so that driver is ready to receive the unsolicited packets and
arm the CQ as soon as FW enable is performed.

Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>