msm: camera: isp: Configure epoch based on FPS only for pix path

We should configure epoch only for pix path. Return success for case
where epoch needs not to be configure i.e RDI only.

Change-Id: I0d10071636005ec4f8f5c37dffa3ce0ced32d790
Signed-off-by: Chandan Kumar Jha <cjha@codeaurora.org>