crypto: ccp - Use scoped guard for mutex

Use a scoped guard to simplify the cleanup handling.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>