ieee802154: ca8210: Fix a potential NULL pointer dereference

'spi' is known to be NULL, so we dereference a NULL pointer here.
Use 'pr_crit()' instead of 'dev_crit()' to report the message.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>