I2C: sample SDA earlier

[bugadani]

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[bugadani]

To be fair, I should probably remove the half_cycle/2 term instead. Technically, we can sample at any point after the rising edge, and scl_wait_high is supposed to be somewhat dependent on the hardware (i.e. it should be tunable, maybe). scl_wait_high represents the rising edge of the clock signal, after which the clock signal is high for scl_high. We should probably aim at the start/middle of the interval covered by scl_high.

Still, this should be good enough to test.