[SCSI] bnx2fc: Call bnx2fc_return_rqe and bnx2fc_get_next_rqe with tgt lock held

tgt lock is needed during -
        bnx2fc_return_rqe to protect the rq_prod_idx.
        bnx2fc_get_next_rqe to protect rq_cons_idx

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>