w1: Only wake up the search process if it is going to be searching

It's valid to set the search count to 0 to stop searching, so don't
wake up the search thread to not search.

Signed-off-by: David Fries <David@Fries.net>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>