Fix AFS to write back dirty on unmounting.  This didn't happen because
afs_super_ops.drop_inode was pointing to generic_delete_inode.  Now this
pointer is left set to NULL so that the default behaviour occurs instead.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>