[CIFS] Don't cache timestamps on utimes due to coarse granularity

[CIFS] Don't cache timestamps on utimes due to coarse granularity

force revalidate of the file when any of the timestamps are set since
some filesytem types do not have finer granularity timestamps and
we can not always detect which file systems round timestamps down
to determine whether we can cache the mtime on setattr
samba bugzilla 3775

Acked-by: Shirish Pargaonkar <sharishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>