fix pioasm python output

[urish]

While working on the online pioasm, I found several PIO instructions that result in invalid python code. Here is a small program that demonstrates the issue:

.program python_issue

    push block
    wait 0 irq 1 rel
    irq clear 1 rel

And the resulting Python program:

# -------------------------------------------------- #
# This file is autogenerated by pioasm; do not edit! #
# -------------------------------------------------- #

import rp2
from machine import Pin
# ----------- #
# python_test #
# ----------- #

@rp2.asm_pio()
def python_test():
    wrap_target()
    push(, block)                         # 0
    wait(0, irq, 1 rel)                   # 1
    irq(clear 1 rel)                      # 2
    wrap()

After this fix, the above program compiles to a valid python syntax:

# -------------------------------------------------- #
# This file is autogenerated by pioasm; do not edit! #
# -------------------------------------------------- #

import rp2
from machine import Pin
# ----------- #
# python_test #
# ----------- #

@rp2.asm_pio()
def python_test():
    wrap_target()
    push(block)                           # 0
    wait(0, irq, rel(1))                  # 1
    irq(clear, rel(1))                    # 2
    wrap()

[kilograham]

Ha, yeah, thought there might be some of these... didn't get a lot of testing as it isn't really used in any actual micropython workflow - just added for completeness/porting

thanks for fixing.