lib: tls_credentials: return size even if too big

The simple backend returns the size of the credential,
even if it is too big.
The secure backend should do the same,
our libraries depend on this behaviour.

Signed-off-by: Maximilian Deubel <maximilian.deubel@nordicsemi.no>

subsys/net/lib/tls_credentials/tls_credentials_trusted.c

@@ -401,6 +401,7 @@ int tls_credential_get(sec_tag_t tag, enum tls_credential_type type,
 
 	if (info.size > *credlen) {
 		ret = -EFBIG;
+		*credlen = info.size;
 		goto cleanup;
 	}