Add missing <string.h> include.

Change-Id: Iec90d46b480f2d08d26d0dde998c6aa164844750
diff --git a/camera/QCamera2/stack/common/cam_types.h b/camera/QCamera2/stack/common/cam_types.h
index 45e7b6e..a1a97fa 100644
--- a/camera/QCamera2/stack/common/cam_types.h
+++ b/camera/QCamera2/stack/common/cam_types.h
@@ -31,6 +31,7 @@
 #define __QCAMERA_TYPES_H__
 
 #include <stdint.h>
+#include <string.h>
 #include <pthread.h>
 #include <inttypes.h>
 #include <media/msmb_camera.h>