ltr502als.c: Modify the way of ALS first data reporting

ltr502als.c: Modify the way of ALS first data reporting

BZ: 17876 18551

1. Previously, when ALS is enabled, it will report zero before the first
interrupt occurs, this may cause incorrect behavior of LED light.  Now
ALS doesn't report any data until the first interrupt occurs.
2. In order to speed up the interrupt triggering, ADC sample integration
circle of ALS is changed to 1.

Signed-off-by: Leo Yan <leo.yan@intel.com>
Change-Id: I25a2d16e9db09cc44a299b127feff8a3f53d4430
Reviewed-on: http://android.intel.com:8080/29959
Reviewed-by: Yan, Leo <leo.yan@intel.com>
Reviewed-by: Liu, Hong <hong.liu@intel.com>
Reviewed-by: Du, Alek <alek.du@intel.com>
Tested-by: Wang, Zhifeng <zhifeng.wang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>