rxrpc: Downgrade the BUG() for unsupported token type in rxrpc_read()

If rxrpc_read() (which allows KEYCTL_READ to read a key), sees a token of a
type it doesn't recognise, it can BUG in a couple of places, which is
unnecessary as it can easily get back to userspace.

Fix this to print an error message instead.

Fixes: 99455153d0 ("RxRPC: Parse security index 5 keys (Kerberos 5)")
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/key.c

@@ -1107,7 +1107,8 @@ static long rxrpc_read(const struct key *key,
 			break;
 
 		default: /* we have a ticket we can't encode */
-			BUG();
+			pr_err("Unsupported key token type (%u)\n",
+			       token->security_index);
 			continue;
 		}
 
@@ -1223,7 +1224,6 @@ static long rxrpc_read(const struct key *key,
 			break;
 
 		default:
-			BUG();
 			break;
 		}