RDMA/bnxt_re: Avoid NULL check after accessing the pointer

This is reported by smatch check.  rcfw->creq_bar_reg_iomem is accessed in
bnxt_qplib_rcfw_stop_irq and this variable check afterwards doesn't make
sense.  Also, rcfw->creq_bar_reg_iomem will never be NULL.  So Removing
this check.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 6e04b103 ("RDMA/bnxt_re: Fix broken RoCE driver due to recent L2 driver changes")
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>