afs: Conditionalise a new unused variable

The bulk readpages support introduced a harmless warning:

fs/afs/file.c: In function 'afs_readpages_page_done':
fs/afs/file.c:270:20: error: unused variable 'vnode' [-Werror=unused-variable]

This adds an #ifdef to match the user of that variable.  The user of the
variable has to be conditional because it accesses a member of a struct
that is also conditional.

Fixes: 91b467e0a3 ("afs: Make afs_readpages() fetch data in bulk")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/afs/file.c

@@ -267,7 +267,9 @@ static int afs_readpage(struct file *file, struct page *page)
  */
 static void afs_readpages_page_done(struct afs_call *call, struct afs_read *req)
 {
+#ifdef CONFIG_AFS_FSCACHE
 	struct afs_vnode *vnode = call->reply;
+#endif
 	struct page *page = req->pages[req->index];
 
 	req->pages[req->index] = NULL;