w1: w1_ds2408.c: quite sparse noise about using plaing integer as NULL pointer

NULL not 0 should be used with pointers. Just remove the offending
lines since they will default to NULL anyway.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>