Qt4: /dev/dvb/adapter is Linux DVB, not just Linux

This is also used on *BSD systems.
(cherry picked from commit 05297483)

modules/gui/qt4/components/open_panels.cpp

@@ -925,7 +925,7 @@ void CaptureOpenPanel::initialize()
 
     dvbCard = new QSpinBox;
     dvbCard->setAlignment( Qt::AlignRight );
-#ifdef __linux__
+#ifdef __unix__
     dvbCard->setPrefix( "/dev/dvb/adapter" );
 #endif
     dvbDevLayout->addWidget( dvbDeviceLabel, 0, 0 );