it821x: fix kzalloc() failure handling

Allocate 'struct it821x_dev' objects for both ports in it821x_init_one().

Fixes potential OOPS in it821x_quirkproc() (uses 'itdev' unconditionally)
and other problems ('itdev' is needed for correct operation of the driver).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>