nilfs2: fix a checkpatch error in page.c

Will correct the following checkpatch error:

 ERROR: trailing whitespace
 #494: FILE: page.c:494:
 + $
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/page.c

@@ -491,7 +491,7 @@ unsigned nilfs_page_count_clean_buffers(struct page *page,
 	}
 	return nc;
 }
- 
+
 void nilfs_mapping_init_once(struct address_space *mapping)
 {
 	memset(mapping, 0, sizeof(*mapping));