make use of qtHaveModule()

Change-Id: I14da5455b7dd4681254e1652395df5f5c65746bd
Reviewed-by: Tasuku Suzuki <stasuku@gmail.com>
Reviewed-by: Jonas Rabbe <jonas.rabbe@gmail.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/plugins/directshow/camera/camera.pri

@@ -23,7 +23,7 @@ SOURCES += \
     $$PWD/dsimagecapturecontrol.cpp \
     $$PWD/dscamerasession.cpp
 
-!isEmpty(QT.widgets.name) {
+qtHaveModule(widgets) {
     HEADERS += $$PWD/dsvideowidgetcontrol.h
     SOURCES += $$PWD/dsvideowidgetcontrol.cpp
 }