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

@@ -850,11 +850,11 @@
          * hang the snapshot on.
          */
         nmnp = mntgetnode(vp);
 
         *vpp = MTOV(nmnp);
-        atomic_add_32(&MTOD(nmnp)->mnt_nopen, 1);
+        atomic_inc_32(&MTOD(nmnp)->mnt_nopen);
         VN_RELE(vp);
         return (0);
 }
 
 /* ARGSUSED */

@@ -873,11 +873,11 @@
         if (vp->v_count == 1) {
                 rw_enter(&mnp->mnt_contents, RW_WRITER);
                 mntfs_freesnap(mnp, &mnp->mnt_read);
                 mntfs_freesnap(mnp, &mnp->mnt_ioctl);
                 rw_exit(&mnp->mnt_contents);
-                atomic_add_32(&MTOD(mnp)->mnt_nopen, -1);
+                atomic_dec_32(&MTOD(mnp)->mnt_nopen);
         }
         return (0);
 }
 
 /* ARGSUSED */