accel/tcg: Don't use TARGET_LONG_BITS in decode_sleb128

accel/tcg: Don't use TARGET_LONG_BITS in decode_sleb128

When we changed decode_sleb128 from target_long to
int64_t, we failed to adjust the shift limit.

Cc: qemu-stable@nongnu.org
Fixes: c9ad8d27caa ("tcg: Widen gen_insn_data to uint64_t")
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 9401f91b9b0c46886388735b3f2033a9c254895a)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>