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

*** 199,209 ****
           */
          vfsp->vfs_bsize = DEV_BSIZE;
          vfsp->vfs_fstype = sharefs_fstype;
          do {
                  dev = makedevice(sharefs_major,
!                     atomic_add_32_nv(&sharefs_minor, 1) & L_MAXMIN32);
          } while (vfs_devismounted(dev));
          vfs_make_fsid(&vfsp->vfs_fsid, dev, sharefs_fstype);
          vfsp->vfs_data = data;
          vfsp->vfs_dev = dev;
  
--- 199,209 ----
           */
          vfsp->vfs_bsize = DEV_BSIZE;
          vfsp->vfs_fstype = sharefs_fstype;
          do {
                  dev = makedevice(sharefs_major,
!                     atomic_inc_32_nv(&sharefs_minor) & L_MAXMIN32);
          } while (vfs_devismounted(dev));
          vfs_make_fsid(&vfsp->vfs_fsid, dev, sharefs_fstype);
          vfsp->vfs_data = data;
          vfsp->vfs_dev = dev;