CHROMIUM: iio: light sensor: Improve granularity of tsl2583 lux values.

CHROMIUM: iio: light sensor: Improve granularity of tsl2583 lux values.

When illuminance0_calibbias gets 4000 (for a 4x multiplier), we see lux
granularity of 4.  Reversing the order of the right shift and multiplication
retains the precision of the unadjusted lux value.

BUG=chromium-os:23451
TEST='while :;do cat illuminance0_input;done' gives granularity of 1.

Signed-off-by: Bryan Freed <bfreed@chromium.org>
Change-Id: I92667cb04007ac17e91e0e3da10d691f774a753d
Reviewed-on: https://gerrit.chromium.org/gerrit/12394
Reviewed-by: Benson Leung <bleung@chromium.org>