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

@@ -612,11 +612,11 @@
          * Direct Writes
          */
 
         if (!exclusive) {
                 ufs_shared_writes++;
-                ncur = atomic_add_32_nv(&ufs_cur_writes, 1);
+                ncur = atomic_inc_32_nv(&ufs_cur_writes);
                 if (ncur > ufs_maxcur_writes)
                         ufs_maxcur_writes = ncur;
         }
 
         /*

@@ -725,11 +725,11 @@
                 as_pageunlock(as, pplist, pglck_base, pglck_size, S_READ);
 
         }
 
         if (!exclusive) {
-                atomic_add_32(&ufs_cur_writes, -1);
+                atomic_dec_32(&ufs_cur_writes);
                 /*
                  * If this write was done shared, readers may
                  * have pulled in unmodified pages. Get rid of
                  * these potentially stale pages.
                  */