w1: IAD Register is yet readable trough iad sys file. Fix snprintf (%u for unsigned, count for max size).

IAD Register is yet readable trough the "iad" sys file.

A write to the "iad" sys file enables or disables the current
measurement, but it was not possible to get the measured value by
reading it.
Fix: %u in snprintf for unsigned values (vdd and vad)
Fix: Avoid possibles overflows (Usage of the 'count' variables)
Signed-off-by: Julien Folly <julien.folly@gmail.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>