Fix qt5-websockets-qml's dependency path in bsd.qt.mk.

libdeclarative_qmlwebsockets.so is not installed into ${QT_LIBDIR}, which
causes the dependency logic in bsd.qt.mk to actually do something equivalent to
this instead:

BUILD_DEPENDS+=  ${QT_LIBDIR}/${QT_QMLDIR}/QtWebSockets/libdeclarative_qmlwebsockets.so:www/qt5-websockets-qml
RUN_DEPENDS+=    ${QT_LIBDIR}/${QT_QMLDIR}/QtWebSockets/libdeclarative_qmlwebsockets.so:www/qt5-websockets-qml

which translates into something like

/usr/local/lib/qt5//usr/local/lib/qt5/qml/QtWebSockets/libdeclarative_qmlwebsockets.so:www/qt5-websockets-qml

which obviously does not exist.

Instead of settin websockets-qml_LIB, set websockets-qml_PATH like we do for
other QML ports, so that our dependency logic does not needlessly prepend
${QT_LIBDIR} there. This fixes devel/qt5's build.

PR: 220045