Update analogin_api.c

Implemented proper self-calibration logic as per UM10732, and changed sampling clock to actually divide by 1 (CLKDIV = 0).
Update analogin_api.c

Implemented proper self-calibration logic as per UM10736.
Merge pull request #522 from neilt6/master

HAL: Better ADC self-calibration for LPC11U6X & LPC15XX