Fix build in 5.1 tree

Change-Id: Id1205f0dda771500f02195c53c5d49bb14c83fac
diff --git a/twrp-functions.cpp b/twrp-functions.cpp
index 945f61d..96163f1 100755
--- a/twrp-functions.cpp
+++ b/twrp-functions.cpp
@@ -1522,7 +1522,7 @@
 	return TW_DEFAULT_RECOVERY_FOLDER;
 }
 
-bool TWFunc::Check_Xml_Format(const std::string filename) {
+bool TWFunc::Check_Xml_Format(const char* filename) {
 	std::string buffer(' ', 4);
 	std::string abx_hdr("ABX\x00", 4);
 	std::ifstream File;