package/qt5webengine: add missing opus dependency

The package opus is selected but it is not listed in the dependencies.

This adds opus to QT5WEBENGINE_DEPENDENCIES.

Fixes:

	$ make qt5webengine
	(...)
	ERROR: Feature 'webengine-system-opus' was enabled, but the pre-condition 'config.unix && libs.webengine-opus' failed.

Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>

package/qt5/qt5webengine/qt5webengine.mk

@@ -78,6 +78,7 @@ QT5WEBENGINE_DEPENDENCIES += \
 	libvpx \
 	libxml2 \
 	libxslt \
+	opus \
 	snappy \
 	webp