pinctrl: ralink: rt2880: return proper error code

Check for NULL shall return '-ENOMEM' instead of '-1'.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201213161721.6514-4-sergio.paracuellos@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>