virtio_fs: Modify format for virtio_fs_direct_access

We should isolate operators with spaces.

Signed-off-by: Deming Wang <[e-mail]>
Signed-off-by: Miklos Szeredi <[e-mail]>

fs/fuse/virtio_fs.c

···
 {
 	struct virtio_fs *fs = dax_get_private(dax_dev);
 	phys_addr_t offset = PFN_PHYS(pgoff);
-	size_t max_nr_pages = fs->window_len/PAGE_SIZE - pgoff;
+	size_t max_nr_pages = fs->window_len / PAGE_SIZE - pgoff;
 
 	if (kaddr)
 		*kaddr = fs->window_kaddr + offset;