QLibrary: fix Clazy warning about QString(const char*)

Wrap dlerror() in QLatin1StringView(), like we already do in
unload_sys().

Amends a6a56814702612d8981f594a6158d70a7928cb99.

Change-Id: Ia8c91d6962c74d5916c47b2abbb3920f051c8e5e
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 097f0edc9ff2a53c55395a5ef9dd20f7763d84b5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/plugin/qlibrary_unix.cpp

@@ -244,7 +244,8 @@ bool QLibraryPrivate::load_sys()
 
     locker.relock();
     if (!hnd) {
-        errorString = QLibrary::tr("Cannot load library %1: %2").arg(fileName, dlerror());
+        errorString = QLibrary::tr("Cannot load library %1: %2").arg(fileName,
+                                                                     QLatin1StringView(dlerror()));
     }
     if (hnd) {
         qualifiedFileName = attempt;