#734 stm32 dac bug when using only channel 2 in direct mode

[alex_31]

the problem is in dac_lld_put_channel function.
the dataoffset is not added in case of use of channel 2 only.
with the hal abstraction model, in case of only channel 2 used, the driver is DACD2 with only one channel (0),
but for the real hardware, the channel is channel 2 and offset has to be add.

adding the offset resolve the problem.

proposal patch is attached

[Giovanni Di Sirio]

Patch applied, thanks.