PKCS#7: fix missing break on OID_sha224 case

The OID_sha224 case is missing a break and it falls through
to the -ENOPKG error default.  Since HASH_ALGO_SHA224 seems
to be supported, this looks like an unintentional missing break.

Fixes: 07f081fb ("PKCS#7: Add OIDs for sha224, sha284 and sha512 hash algos and use them")
Cc: <stable@vger.kernel.org> # 4.2+
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>