vfs: prefer ->dentry->d_sb to ->mnt->mnt_sb

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/acct.c b/kernel/acct.c
index 8cba124..9663eb8 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -315,7 +315,7 @@
 	spin_lock(&acct_lock);
 restart:
 	list_for_each_entry(acct, &acct_list, list)
-		if (acct->file && acct->file->f_path.mnt->mnt_sb == sb) {
+		if (acct->file && acct->file->f_path.dentry->d_sb == sb) {
 			acct_file_reopen(acct, NULL, NULL);
 			goto restart;
 		}