msm: camera: sensor: remove valid position from actuator driver

Valid_position is no more needed to set the default position to
the inital code.
The userspace handles the same via set_position call.

Change-Id: I4e2024fd139ff8f57fd87d2171ba4f6fc28b4d79
Signed-off-by: Vasko Kalanoski <vaskok@codeaurora.org>