audio: dbus requires pixman

Commit commit 6cc5a61 ("ui/dbus: win32 support") has broken audio/dbus
compilation when pixman is not included.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1739

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230630214156.2181558-1-marcandre.lureau@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

audio/meson.build

@@ -31,7 +31,7 @@ endforeach
 
 if dbus_display
     module_ss = ss.source_set()
-    module_ss.add(when: gio, if_true: files('dbusaudio.c'))
+    module_ss.add(when: [gio, pixman], if_true: files('dbusaudio.c'))
     audio_modules += {'dbus': module_ss}
 endif