Do not update calibsense if prop read fails

Do not update calibsense if prop read fails

 It was observed that in case the android prop read fails,
 we write a 0 value(typically happens in case the property variable
 not present)into the sysfs variable. This caused the resulting ALS
 output to be 0, added a check to filter that condition. Now in case
 the read from the android property fails, we just keep the default
 value for the calibsense variable.

 Issue:GMIN-671

Change-Id: Ifd65f0268dfa345ecf8cd6d40255c1a1fd52a03c
Signed-off-by: suyyala <sridhar.uyyala@intel.com>