drivers: adc: stm32: Perform calibration if set in sequence
drivers: adc: stm32: Perform calibration if set in sequence

The calibration bit previously did nothing.

Move calibration to allow call in start_read.

Signed-off-by: Lasse Sangild <34e5df09933f1da4588035dbf790109bb77e3bba@gmail.com>

galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr