msm: camera: flash: Validate the power setting size

Validate the power setting size before copying.
If userspace sends a value which is greater than
MAX_POWER_CONFIG, then the driver accesses unintended memory.
This change will fix the issue.

CRs-Fixed: 1093232
Signed-off-by: Rajesh Bondugula <rajeshb@codeaurora.org>
Change-Id: Ia49963248a94765baa19695294b197ea6f3bb8e2