msm: camera: sensor: Validate step_boundary

step_boundary can take values upto the total_steps
Validate the step_boundary before consuming it.
Convert the type of step_index and region_index to uint16_t
step_index and region_index cannot be negative.

CRs-Fixed: 1001092
Change-Id: I1f23fd6f28bb897824a1ef99a8873b9f986eee70
Signed-off-by: Rajesh Bondugula <rajeshb@codeaurora.org>