Missing used timer def in OMNIBUS target

[flybabo]

While reviewing the code, I found out that TIM_N(8) is missing at USED_TIMERS defined in OMNIBUS/target.h.
Apparently, TIM8 is used in timerHardware[] @target.c.

[flybabo]

I also found out that I2C3_SDA pin is incorrectly defined at drivers/bus_i2c_hal.c.
It must be PC9 not PB4.

[digitalentity]

@flybabo good catch. Can you submit a PR to fix it?

[fiam]

This is no longer relevant. Since #3120, the targets don't need to list the used timers.