msm: camera: Initialize the regulator pointer in the probe

Initialize the regulator pointer in the probe rather than in
init as init is reiterant function and similarly initialize
the pointer to NULL once the regulator_put is called.

Change-Id: I22005e7c6a3beba8cf4918ab789282763443dfca
Signed-off-by: Viswanadha Raju Thotakura <viswanad@codeaurora.org>