Camera3: Reset postproc state correctly during stop

The picture channel stop does stop post-processor
but this is not getting reflected in the
'mPostProcStarted' variable.

Bug: 18230299
Change-Id: I190192e9503de936ff8b6464dbc9b1e333db9597
diff --git a/camera/QCamera2/HAL3/QCamera3Channel.cpp b/camera/QCamera2/HAL3/QCamera3Channel.cpp
index e3d9881..63bc787 100644
--- a/camera/QCamera2/HAL3/QCamera3Channel.cpp
+++ b/camera/QCamera2/HAL3/QCamera3Channel.cpp
@@ -1528,7 +1528,7 @@
     }
 
     m_postprocessor.stop();
-
+    mPostProcStarted = false;
     rc |= QCamera3Channel::stop();
     return rc;
 }