msm: camera: isp: Fix recovery in dual vfe mode

In case of dual vfe overflow recovery fails as
driver is trying to recover from each vfe events.
This by fixed by ignoring overflow event if previous
event handling is ongoing.

Change-Id: Ice89cdc7315bd9ef7deb7bba7a34f88004b4e536
Signed-off-by: Srikanth Uyyala <suyyala@codeaurora.org>