msm: camera: isp: Fix the framedrop setting issue

This change fixes a framedrop issue due to unsynced epoch signal.
In dual vfe case, the epoch signal from each VFE might arrived in any
order. Since reset the framedrop pattern for both VFE is done in the
epocch signal, we need to align this action with the last vfe epoch
signal. The current implementation is to do the reset always on the
vfe1 signal, this has led to incorrect framedrop pattern reset which
cause the framedrop pattern out of sync between two VFEs.
This change aligns this action with the latest epoch signal so split
will not happen.

CRs-fixed: 991080
Change-Id: I20a911fd8cec9e36e6867fa19428513f36054a8a
Signed-off-by: Jing Zhou <jzhou70@codeaurora.org>