pinctrl/: at91: fix warnings

/opt/work/linux-2.6/drivers/pinctrl/pinctrl-at91.c: In function 'at91_pinctrl_probe_dt':
/opt/work/linux-2.6/drivers/pinctrl/pinctrl-at91.c:952:12: warning: assignment discards qualifiers from pointer target type
/opt/work/linux-2.6/drivers/pinctrl/pinctrl-at91.c: In function 'at91_gpio_probe':
/opt/work/linux-2.6/drivers/pinctrl/pinctrl-at91.c:1517:17: warning: assignment discards qualifiers from pointer target type

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>