5045 use atomic_{inc,dec}_* instead of atomic_add_*

*** 316,326 ****
  
          /*
           * We now hold the prom_cpu lock.  Increment the hold count by one
           * and assert our current state before returning to the caller.
           */
!         atomic_add_32(&prom_holdcnt, 1);
          ASSERT(prom_holdcnt >= 1);
          prom_thread = curthread;
  }
  
  /*
--- 316,326 ----
  
          /*
           * We now hold the prom_cpu lock.  Increment the hold count by one
           * and assert our current state before returning to the caller.
           */
!         atomic_inc_32(&prom_holdcnt);
          ASSERT(prom_holdcnt >= 1);
          prom_thread = curthread;
  }
  
  /*
*** 343,353 ****
  
          if (prom_holdcnt == 0)
                  panic("kern_postprom: prom_holdcnt == 0, owner=%p",
                      (void *)prom_cpu);
  
!         if (atomic_add_32_nv(&prom_holdcnt, -1) != 0)
                  return; /* prom lock is held recursively by this CPU */
  
          if ((boothowto & RB_DEBUG) && prom_exit_enter_debugger)
                  kmdb_enter();
  
--- 343,353 ----
  
          if (prom_holdcnt == 0)
                  panic("kern_postprom: prom_holdcnt == 0, owner=%p",
                      (void *)prom_cpu);
  
!         if (atomic_dec_32_nv(&prom_holdcnt) != 0)
                  return; /* prom lock is held recursively by this CPU */
  
          if ((boothowto & RB_DEBUG) && prom_exit_enter_debugger)
                  kmdb_enter();