libobs-opengl: Use bfree instead of free

The variable is allocated with a bmalloc -- not a malloc.

Closes jp9000/obs-studio#473

libobs-opengl/gl-x11.c

@@ -375,7 +375,7 @@ fail_context_create:
 fail_load_gl:
 	XCloseDisplay(display);
 fail_display_open:
-	free(plat);
+	bfree(plat);
 	plat = NULL;
 success:
 	UNUSED_PARAMETER(adapter);