package/qt6/qt6multimedia: fix ffmpeg configure option typo

Buildroot commit 553c55e9bd3cfa05cb84fa4cdfc5d25d51c3486b added this
package with a typo in the configure option to disable ffmpeg support.

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/qt6/qt6multimedia/qt6multimedia.mk

@@ -67,7 +67,7 @@ ifeq ($(BR2_PACKAGE_QT6MULTIMEDIA_FFMPEG),y)
 QT6MULTIMEDIA_CONF_OPTS += -DFEATURE_ffmpeg=ON
 QT6MULTIMEDIA_DEPENDENCIES += ffmpeg
 else
-QT6MULTIMEDIA_CONF_OPTS += -DFEATURE_ffmpeg=ON
+QT6MULTIMEDIA_CONF_OPTS += -DFEATURE_ffmpeg=OFF
 endif
 
 ifeq ($(BR2_PACKAGE_QT6MULTIMEDIA_GSTREAMER),y)