ext4crypt: add missing cflag

Avoid calling e4crypt_prepare_user_storage with wrong input parameters.

Change-Id: I5c8945370cb642e46f08c65090c0290c15fe0b57
libc: Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 632 (recovery), pid 564 (recovery)
diff --git a/crypto/ext4crypt/Decrypt.cpp b/crypto/ext4crypt/Decrypt.cpp
index 3eeaaf8..e69b647 100644
--- a/crypto/ext4crypt/Decrypt.cpp
+++ b/crypto/ext4crypt/Decrypt.cpp
@@ -1336,7 +1336,11 @@
 		printf("e4crypt_unlock_user_key returned fail\n");
 		return false;
 	}
-	if (!e4crypt_prepare_user_storage(nullptr, user_id, 0, flags)) {
+#ifdef USE_KEYSTORAGE_4
+		if (!e4crypt_prepare_user_storage("", user_id, 0, flags)) {
+#else
+		if (!e4crypt_prepare_user_storage(nullptr, user_id, 0, flags)) {
+#endif
 		printf("failed to e4crypt_prepare_user_storage\n");
 		return false;
 	}