raspberrypi: Honor the requested offset= of a StateMachine

[jepler]

The logic to do this was lost in my recent re-organization. Happily, just setting this field appropriately fixes it.

[jepler]

Testing performed: I was using an implementation of quadrature encoder that required being loaded at address 0. It was loaded at address 4(?) instead, because loading at higher addresses is favored, and it didn't work.

You can test with something like

import array
import rp2pio
sm = rp2pio.StateMachine(array.array('H', [0]), 0, offset=1)
assert sm.offset == 1

[dhalbert]

Thanks for spotting this!