AFS: Fix compilation warning

Fix the following warning:

  fs/afs/dir.c: In function 'afs_d_revalidate':
  fs/afs/dir.c:567: warning: 'fid.vnode' may be used uninitialized in this function
  fs/afs/dir.c:567: warning: 'fid.unique' may be used uninitialized in this function

by marking the 'fid' variable as an uninitialized_var.  The problem is
that gcc doesn't always manage to work out that fid is always set on the
path through the function that uses it.

Cc: linux-afs@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/afs/dir.c

@@ -564,7 +564,7 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
 static int afs_d_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
 	struct afs_vnode *vnode, *dir;
-	struct afs_fid fid;
+	struct afs_fid uninitialized_var(fid);
 	struct dentry *parent;
 	struct key *key;
 	void *dir_version;