tcg: Fix info_in_idx increment in layout_arg_by_ref

tcg: Fix info_in_idx increment in layout_arg_by_ref

Off by one error, failing to take into account that layout_arg_1
already incremented info_in_idx for the first piece.  We only
need care for the n-1 TCG_CALL_ARG_BY_REF_N pieces here.

Cc: qemu-stable@nongnu.org
Fixes: 313bdea84d2 ("tcg: Add TCG_CALL_{RET,ARG}_BY_REF")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1751
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Peter Maydell <peter.maydell@linaro.org>