Change additional tcg_const_tl to tcg_constant_tl

Note that gen_pred_cancal had slot_mask initialized with tcg_const_tl.
However, it is not constant throughout, so we initialize it with
tcg_temp_new and replace the first use with the constant value.

Inspired-by: Richard Henderson <richard.henderson@linaro.org>
Inspired-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>