pan/bi: use unreachable instead of DBG + assert

This error isn't particularly interesting to be able to toggle at
runtime. Let's just use the unreachable macro instead.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33710>

src/panfrost/compiler/bifrost_compile.c

@@ -3379,9 +3379,7 @@ bifrost_tex_format(enum glsl_sampler_dim dim)
       return 0;
 
    default:
-      DBG("Unknown sampler dim type\n");
-      assert(0);
-      return 0;
+      unreachable("Unknown sampler dim type\n");
    }
 }