bus: arm-ccn: Simplify code

Use 'devm_kasprintf()' to simplify the code.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>