cifs: have cifs_NTtimeToUnix take a little-endian arg

...and just have the function call le64_to_cpu.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>