[ImportVerilog] Properly cast subroutine call result value

[maerhart]

error.txt diff

9a10
>   36 error: failed to legalize operation 'moore.builtin.time'
13d13
<   34 error: failed to legalize operation 'moore.builtin.time'
266,267d265
<    1 error: 'moore.xor' op requires the same type for all operands and results
<    1 error: 'moore.mul' op requires the same type for all operands and results

[fabianschuiki]

Nice catch! 🙌 LGTM