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

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

Fixes: deee69a19fd ("target/hppa: Convert memory management insns")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/target/hppa/translate.c b/target/hppa/translate.c
index f3b17ba..bb1b65f 100644
--- a/target/hppa/translate.c
+++ b/target/hppa/translate.c
@@ -2297,7 +2297,7 @@
     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));