AFS: fix a couple of problems with unlinking AFS files

Fix a couple of problems with unlinking AFS files.

 (1) The parent directory wasn't being updated properly between unlink() and
     the following lookup().

     It seems that, for some reason, invalidate_remote_inode() wasn't
     discarding the directory contents correctly, so this patch calls
     invalidate_inode_pages2() instead on non-regular files.

 (2) afs_vnode_deleted_remotely() should handle vnodes that don't have a
     source server recorded without oopsing.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>