pkcs7: Change a pr_warn() to pr_warn_once()

Only display the "PKCS7: Waived invalid module sig (has authattrs)" once.

Suggested-by: Lenny Szubowicz <lszubowi@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Lenny Szubowicz <lszubowi@redhat.com>
cc: Lukas Wunner <lukas@wunner.de>
cc: Ignat Korchagin <ignat@cloudflare.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: Stephan Mueller <smueller@chronox.de>
cc: Eric Biggers <ebiggers@kernel.org>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: keyrings@vger.kernel.org
cc: linux-crypto@vger.kernel.org

crypto/asymmetric_keys/pkcs7_verify.c

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 519eecf..474e2c1 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -427,7 +427,7 @@ int pkcs7_verify(struct pkcs7_message *pkcs7,
 		if (pkcs7->have_authattrs) {
 #ifdef CONFIG_PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
 			if (pkcs7->authattrs_rej_waivable) {
-				pr_warn("Waived invalid module sig (has authattrs)\n");
+				pr_warn_once("Waived invalid module sig (has authattrs)\n");
 				break;
 			}
 #endif