Find /dev/dri/card path that exists (the first one)

include/capture/xcomposite_vaapi.h

@@ -11,6 +11,7 @@ typedef struct {
     Window window;
     bool follow_focused; /* If this is set then |window| is ignored */
     vec2i region_size; /* This is currently only used with |follow_focused| */
+    const char *card_path; /* reference */
 } gsr_capture_xcomposite_vaapi_params;
 
 gsr_capture* gsr_capture_xcomposite_vaapi_create(const gsr_capture_xcomposite_vaapi_params *params);