crypto: artpec6 - Fix printk warning on size_t/%d

Switch to %zu instead of %d for printing size_t.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>