QPluginParsedMetaData: avoid the indirection through QCborMap

value[x] is the same as value.toMap()[x] but avoids the refcounting up
and down just to call the operator[] overload. We're calling the
operator[] overload taking an integer, which means it could match an
array, but we know the data member won't be one because of how
QPluginParsedMetaData::parse() parses.

Change-Id: I2cffe62afda945079b63fffd16bd5c690b2bfee4
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/plugin/qfactoryloader_p.h

@@ -90,7 +90,7 @@ public:
 
     // if data is not a map, toMap() returns empty, so shall these functions
     QCborMap toCbor() const                         { return data.toMap(); }
-    QCborValue value(QtPluginMetaDataKeys k) const  { return toCbor()[int(k)]; }
+    QCborValue value(QtPluginMetaDataKeys k) const  { return data[int(k)]; }
 };
 
 class QFactoryLoaderPrivate;