Camera: Add missing initialization

There is a missing initialization for the member variable.
Initialize the variable with default value.

Test: build libcameraservice
Change-Id: I4981302d5d861923b29df801f5a867339b279a87
diff --git a/services/camera/libcameraservice/device3/Camera3Device.cpp b/services/camera/libcameraservice/device3/Camera3Device.cpp
index 74dbe27..3ff985d 100644
--- a/services/camera/libcameraservice/device3/Camera3Device.cpp
+++ b/services/camera/libcameraservice/device3/Camera3Device.cpp
@@ -2930,6 +2930,7 @@
         mDoPause(false),
         mPaused(true),
         mNotifyPipelineDrain(false),
+        mPrevTriggers(0),
         mFrameNumber(0),
         mLatestRequestId(NAME_NOT_FOUND),
         mCurrentAfTriggerId(0),