msm: camera: isp: Do not enable the ppi hw twice

In case of dual vfe, ppi irq are getting enabled twice. PHY
and PPI will be same for both CSID as only one sensor is streaming the
data.
If the ppi is already enabled, do not enable the ppi for second csid.

Change-Id: I9fdcc44511ce89a660b47893deb4f806d211e029
Signed-off-by: Gaurav Jindal <gjindal@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>