arcnet: Add NULL check in com20020pci_probe()

arcnet: Add NULL check in com20020pci_probe()

devm_kasprintf() returns NULL when memory allocation fails. Currently,
com20020pci_probe() does not check for this case, which results in a
NULL pointer dereference.

Add NULL check after devm_kasprintf() to prevent this issue and ensure
no resources are left allocated.

Fixes: 6b17a597fc2f ("arcnet: restoring support for multiple Sohard Arcnet cards")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
Link: https://patch.msgid.link/20250402135036.44697-1-bsdhenrymartin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>