ARM: dts: at91: at91sam9rl: fix ADC triggers

The triggers for the ADC were taken from at91sam9260 dtsi but are not
correct.

Fixes: a4c1d6c7 ("ARM: at91/dt: sam9rl: add lcd, adc, usb gadget and pwm support")
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201128222818.1910764-10-alexandre.belloni@bootlin.com