For at91 boards, there are different IPs for adc. Different IPs has different
STARTUP & PRESCAL mask in ADC_MR.
Signed-off-by: NJosh Wu <josh.wu@atmel.com>
Acked-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>