Fix manual focus for A2200 cameras

The chdkptp command sequence in the default function does not set manual focus properly for A2200 cameras. Instead, a focus value is determined by the camera's autofocus at the time when capture begins. The configuration option for focus is effectively ignored.

This patch overrides the default function for A2200 cameras and executes a command sequence that is verified to properly set the focus according to configuration. This is verified to work properly on CHDK 1.3 with chdkptp 2.6.