pinctrl: axp209: account for const type of of_device_id.data

The return value of of_device_get_match_data has type const void *.
The desc field of the pctl structure also has a const type, so there
is no need for the const-discarding cast between them.

Done using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>