st/dri: constify dri_fill_st_visual's screen

As the function says - only the visual is changed.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/state_trackers/dri/dri_screen.c

@@ -302,7 +302,8 @@ dri_fill_in_modes(struct dri_screen *screen)
  * Roughly the converse of dri_fill_in_modes.
  */
 void
-dri_fill_st_visual(struct st_visual *stvis, struct dri_screen *screen,
+dri_fill_st_visual(struct st_visual *stvis,
+                   const struct dri_screen *screen,
                    const struct gl_config *mode)
 {
    memset(stvis, 0, sizeof(*stvis));

src/gallium/state_trackers/dri/dri_screen.h

@@ -127,7 +127,8 @@ dri_with_format(__DRIscreen * sPriv)
 }
 
 void
-dri_fill_st_visual(struct st_visual *stvis, struct dri_screen *screen,
+dri_fill_st_visual(struct st_visual *stvis,
+                   const struct dri_screen *screen,
                    const struct gl_config *mode);
 
 void