Fix compilation with QT_RESTRICTED_CAST_FROM_ASCII

Fix the QString constructor used for restricted casts
from char *.

Change-Id: Id7e71f6d0bcd4627bb44b2bd6d6790be2b6ed976
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/corelib/text/qstring.h

@@ -804,7 +804,7 @@ public:
 #if defined(QT_RESTRICTED_CAST_FROM_ASCII)
     template <int N>
     inline QString(const char (&ch)[N])
-        : d(fromAscii_helper(ch, N - 1))
+        : QString(fromUtf8(ch))
     {}
     template <int N>
     QString(char (&)[N]) = delete;