pinctrl: imx: Check for memory allocation failure

If 'devm_kzalloc' fails, a NULL pointer will be dereferenced.
Return -ENOMEM instead, as done for the other memory allocation just a
few lines below.
BTW, change the 'devm_kzalloc' into a 'devm_kcalloc'.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>