pinctrl: ralink: Check for null return of devm_kcalloc

In the Linux kernel, the following vulnerability has been resolved:

pinctrl: ralink: Check for null return of devm_kcalloc

Because of the possible failure of the allocation, data->domains might be NULL pointer and will cause the dereference of the NULL pointer later. Therefore, it might be better to check it and directly return -ENOMEM without releasing data manually if fails, because the comment of the devm_kmalloc() says "Memory allocated with this function is automatically freed on driver detach.".