RDMA/bnxt_re: Dereg MR in FW before freeing the fast_reg_page_list

If the host buffers are freed before destroying MR in HW,
HW could try accessing these buffers. This could cause a host
crash. Fixing the code to avoid this condition.

Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>