Fix style of "const".

libdevcore/UTF8.cpp

@@ -77,7 +77,7 @@ bool isWellFormed(unsigned char byte1, unsigned char byte2)
 	return false;
 }
 
-bool validateUTF8(const unsigned char *_input, size_t _length, size_t& _invalidPosition)
+bool validateUTF8(unsigned char const* _input, size_t _length, size_t& _invalidPosition)
 {
 	bool valid = true;
 	size_t i = 0;