KEYS: trusted: Do not use WARN when encode fails

When asn1_encode_sequence() fails, WARN is not the correct solution.

1. asn1_encode_sequence() is not an internal function (located
   in lib/asn1_encode.c).
2. Location is known, which makes the stack trace useless.
3. Results a crash if panic_on_warn is set.

It is also noteworthy that the use of WARN is undocumented, and it
should be avoided unless there is a carefully considered rationale to
use it.

Replace WARN with pr_err, and print the return value instead, which is
only useful piece of information.

Cc: stable@vger.kernel.org # v5.13+
Fixes: f221974 ("security: keys: trusted: use ASN.1 TPM2 key format for the blobs")
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Author: jarkkojs

security/keys/trusted-keys/trusted_tpm2.c

@@ -84,8 +84,9 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 	work1 = payload->blob;
 	work1 = asn1_encode_sequence(work1, work1 + sizeof(payload->blob),
 				     scratch, work - scratch);
-	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed")) {
+	if (IS_ERR(work1)) {
 		ret = PTR_ERR(work1);
+		pr_err("BUG: ASN.1 encoder failed with %d\n", ret);
 		goto err;
 	}