CIFS: Fix possible data coherency problem after oplock break to None

by using cifs_invalidate_mapping rather than invalidate_remote_inode
in cifs_oplock_break - this invalidates all inode pages and resets
fscache cookies.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>