mfd: sun4i-gpadc: Constify static struct resource

Constify adc_resources[]. The only usage is to assign its address to the
resources field of the mfd_cell struct. This allows the compiler to put
it in read-only memory. Done with the help of Coccinelle.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>