gpio: fix constconst in devres

Commit 1feb57a2
"gpio: add parameter to allow the use named gpios"
includes a double-consted array. What we want is not
const const * but const * const (const pointer to const
data). Fix this.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Olliver Schinagl <oliver@schinagl.nl>
Cc: Rojhalat Ibrahim <imr@rtschenk.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>