Be more C++. volume UUID should always be std::string.

Test: boots
Bug: 67041047
Change-Id: I36d3944ae8de192703b9ee359900841b833fe3a1
diff --git a/fs/Ext4.cpp b/fs/Ext4.cpp
index 0cf4f9e..1898155 100644
--- a/fs/Ext4.cpp
+++ b/fs/Ext4.cpp
@@ -42,6 +42,7 @@
 #include <android-base/stringprintf.h>
 #include <cutils/log.h>
 #include <cutils/properties.h>
+#include <ext4_utils/ext4_crypt.h>
 #include <logwrap/logwrap.h>
 #include <selinux/selinux.h>