fb: remove unnecessary casts

src/plugins/platforms/fbdev/fb_backend.cpp

@@ -103,11 +103,14 @@ bool FramebufferBackend::initialize()
 {
     setSoftwareCursorForced(true);
 
-    QString framebufferDevice = deviceIdentifier().constData();
+    QByteArray framebufferDevice = deviceIdentifier();
     if (framebufferDevice.isEmpty()) {
-        framebufferDevice = QString(Udev().listFramebuffers().at(0)->devNode());
+        const auto fbs = Udev().listFramebuffers();
+        if (fbs.size() > 0) {
+            framebufferDevice = fbs.at(0)->devNode();
+        }
     }
-    int fd = open(framebufferDevice.toUtf8().constData(), O_RDWR | O_CLOEXEC);
+    int fd = open(framebufferDevice.constData(), O_RDWR | O_CLOEXEC);
     qCDebug(KWIN_FB) << "Using frame buffer device:" << framebufferDevice;
     if (fd < 0) {
         qCWarning(KWIN_FB) << "failed to open frame buffer device:" << framebufferDevice;