[PATCH] fuse: fix zero timeout

An attribute and entry timeout of zero should mean, that the entity is
invalidated immediately after the operation.  Previously invalidation only
happened at the next clock tick.

Reported and tested by Craig Davies.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>