adt7470: observe the number of temperature sensors to shorten update time

The adt7470 driver currently assumes that 1s is the proper time to wait to
read all temperature sensors.  However, the correct time is 200ms *
number_of_sensors.  This patch sets the default time to provide for 10
sensors and then lowers it based on the number of sensor inputs that have
nozero values.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>