5083 avoid undefined order of operations in assignments

*** 1781,1791 ****
          if (rb_head->state == SGHSC_RB_FULL)
                  return (DDI_FAILURE);
  
          rb_head->buf[rb_head->put_idx] = *event;
  
!         rb_head->put_idx = ++rb_head->put_idx & (rb_head->size - 1);
  
          if (rb_head->put_idx == rb_head->get_idx)
                  rb_head->state = SGHSC_RB_FULL;
          else
                  rb_head->state = SGHSC_RB_FLOAT;
--- 1781,1791 ----
          if (rb_head->state == SGHSC_RB_FULL)
                  return (DDI_FAILURE);
  
          rb_head->buf[rb_head->put_idx] = *event;
  
!         rb_head->put_idx = (rb_head->put_idx + 1) & (rb_head->size - 1);
  
          if (rb_head->put_idx == rb_head->get_idx)
                  rb_head->state = SGHSC_RB_FULL;
          else
                  rb_head->state = SGHSC_RB_FLOAT;
*** 1804,1814 ****
          if (rb_head->state == SGHSC_RB_EMPTY)
                  return (DDI_FAILURE);
  
          *event = rb_head->buf[rb_head->get_idx];
  
!         rb_head->get_idx = ++rb_head->get_idx & (rb_head->size - 1);
  
          if (rb_head->get_idx == rb_head->put_idx)
                  rb_head->state = SGHSC_RB_EMPTY;
          else
                  rb_head->state = SGHSC_RB_FLOAT;
--- 1804,1814 ----
          if (rb_head->state == SGHSC_RB_EMPTY)
                  return (DDI_FAILURE);
  
          *event = rb_head->buf[rb_head->get_idx];
  
!         rb_head->get_idx = (rb_head->get_idx + 1) & (rb_head->size - 1);
  
          if (rb_head->get_idx == rb_head->put_idx)
                  rb_head->state = SGHSC_RB_EMPTY;
          else
                  rb_head->state = SGHSC_RB_FLOAT;