Add missing <string.h> include.

Change-Id: I2a42097daf5a68ef8c75e5b8ca93f23219bfa152
diff --git a/camera/QCamera2/stack/common/cam_types.h b/camera/QCamera2/stack/common/cam_types.h
index aab081c..3c86ea7 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>