9p: fix build breakage introduced by FS-Cache

While building 2.6.32-rc8-git2 for Fedora I noticed the following thinko
in commit 201a15428bd54f83eccec8b7c64a04b8f9431204 ("FS-Cache: Handle
pages pending storage that get evicted under OOM conditions"):

  fs/9p/cache.c: In function '__v9fs_fscache_release_page':
  fs/9p/cache.c:346: error: 'vnode' undeclared (first use in this function)
  fs/9p/cache.c:346: error: (Each undeclared identifier is reported only once
  fs/9p/cache.c:346: error: for each function it appears in.)
  make[2]: *** [fs/9p/cache.o] Error 1

Fix the 9P filesystem to correctly construct the argument to
fscache_maybe_release_page().

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Xiaotian Feng <dfeng@redhat.com> [from identical patch]
Signed-off-by: Stefan Lippers-Hollmann <s.l-h@gmx.de> [from identical patch]
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/9p/cache.c

@@ -343,7 +343,7 @@ int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
 
 	BUG_ON(!vcookie->fscache);
 
-	return fscache_maybe_release_page(vnode->cache, page, gfp);
+	return fscache_maybe_release_page(vcookie->fscache, page, gfp);
 }
 
 void __v9fs_fscache_invalidate_page(struct page *page)