iio:adc:at91-sama5d2: fix vref_uv type

vref_uv has to be an int.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
1 file changed