bh1721: delay first read after light sensor enable

Light sensor was delaying first time read to
poll delay milli seconds. This fix changes the
first time read delay to 50 milli seconds.
bh1721: set poll_delay to DELAY_LOWBOUND when new delay < DELAY_LOWBOUND

If a delay of 0 or some low value is passed from any apps,
then system can lock up.
input: bh1721: Pass lightsensor max and fuzz values in platform data.