hal_reg_write_need_delay is invoked immediately after
q_elem->valid check. The first two instructions in
hal_reg_write_need_delay could be in the CPU instruction
pipeline which could result in possible loading and
dereferencing of NULL srng from an invalid q_elem.
Fix is to invoke hal_reg_write_need_delay just before
hal_process_reg_write_q_elem and also add NULL checks
to avoid the srng NULL pointer dereference.
Change-Id: I2de50b1e78782e3c91a9cb4477f28d91f9c29439
CRs-Fixed: 2973257
8ddd31db96