CameraWrapper: set sony-focus-area correctly

When we touch the screen to set a focus area, this
parameter needs to be set to "user" instead of the
default value "center".
This is the behavior of stock Camera app, but it's
not making significant improvements here...just to
make sure it does not go wrong.

Change-Id: I0bdf320067d571fdb5619a2a4ba1feb8ace15edf