Staging: comedi: addi-data: NULL dereference of amcc in v_pci_card_list_init()

amcc allocation may fail, prevent a NULL dereference.

allocation may fail, prevent a dereference.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>