frontends/dri: always init opencl_func_mutex in InitScreen hooks

this otherwise leads to a mismatch where some types of screen may have
the mutex initialized while others don't, in which case dri_release_screen()
will attempt to destroy an uninitialized mutex

cc: mesa-stable

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29021>

src/gallium/frontends/dri/drisw.c

@@ -582,6 +582,8 @@ drisw_init_screen(struct dri_screen *screen, bool driver_name_is_inferred)
    struct pipe_screen *pscreen = NULL;
    const struct drisw_loader_funcs *lf = &drisw_lf;
 
+   (void) mtx_init(&screen->opencl_func_mutex, mtx_plain);
+
    screen->swrast_no_present = debug_get_option_swrast_no_present();
 
    if (loader->base.version >= 4) {

src/gallium/frontends/dri/kopper.c

@@ -116,6 +116,8 @@ kopper_init_screen(struct dri_screen *screen, bool driver_name_is_inferred)
    const __DRIconfig **configs;
    struct pipe_screen *pscreen = NULL;
 
+   (void) mtx_init(&screen->opencl_func_mutex, mtx_plain);
+
    if (!screen->kopper_loader) {
       fprintf(stderr, "mesa: Kopper interface not found!\n"
                       "      Ensure the versions of %s built with this version of Zink are\n"