CameraSettings: Fix crash when HAL has too many exposure steps

Most of the exposure code works with arbitrary ranges, but the
icons that are presented to the user to choose a value are limited
to the -5..5 range, so take only those into account...

Change-Id: I9eb0b7fc92373d61c93ec7215fcb43dfc574b62c
Merge remote branch 'cm/cm-10.1'