scsi: bnx2i: missing error code in bnx2i_ep_connect()

If bnx2i_map_ep_dbell_regs() then we accidentally return NULL instead of
an error pointer.  It results in a NULL dereference in
iscsi_if_ep_connect().

Fixes: cf4e6363 ("[SCSI] bnx2i: Add bnx2i iSCSI driver.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>