[CIFS] mtime bounces from local to remote when cifs nocmtime i_flags overwritten

atime flag was also overwritten. Noticed by Shirish when he was debugging
an atime problem.  Should help performance a bit too.

cifs should be getting time stamps from the server (that was the original
intent too)

Signed-off-by: Steve French <sfrench@us.ibm.com>