egl/wayland: Always initialise fd_display_gpu

Set it to an invalid value, rather than leaving it to be stdout or
something.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24347>

src/egl/drivers/dri2/platform_wayland.c

@@ -2826,6 +2826,7 @@ dri2_initialize_wayland_swrast(_EGLDisplay *disp)
       return _eglError(EGL_BAD_ALLOC, "eglInitialize");
 
    dri2_dpy->fd_render_gpu = -1;
+   dri2_dpy->fd_display_gpu = -1;
    disp->DriverData = (void *)dri2_dpy;
 
    if (dri2_wl_formats_init(&dri2_dpy->formats) < 0)