Address a few compiler warnings

Change-Id: I6e063fba8d58c8c53da6bca6292c84e3392aee50
diff --git a/twrpDigest.cpp b/twrpDigest.cpp
index c3cff71..8380d2c 100644
--- a/twrpDigest.cpp
+++ b/twrpDigest.cpp
@@ -86,7 +86,7 @@
 }
 
 int twrpDigest::read_md5digest(void) {
-	int i = 0;
+	size_t i = 0;
 	bool foundMd5File = false;
 	string md5file = "";
 	vector<string> md5ext;