target/hppa: Use only low 2 immediate bits for PROBEI

During the conversion to decodetree, the 2-bit mask was lost.

Fixes: deee69a ("target/hppa: Convert memory management insns")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/hppa/translate.c

@@ -2297,7 +2297,7 @@ static bool trans_probe(DisasContext *ctx, arg_probe *a)
     form_gva(ctx, &addr, &ofs, a->b, 0, 0, 0, a->sp, 0, false);
 
     if (a->imm) {
-        level = tcg_constant_i32(a->ri);
+        level = tcg_constant_i32(a->ri & 3);
     } else {
         level = tcg_temp_new_i32();
         tcg_gen_extrl_i64_i32(level, load_gpr(ctx, a->ri));