msm: camera: fd: move start cmd to post config

submit start register value along with others to make
sure hw start only when all the register values are
submitted by CDM.

Change-Id: I8e99b0c5ac1a7e2cdd713914f2c7dd0797e45b0d
Signed-off-by: Junzhe Zou <jnzhezou@codeaurora.org>