Use acpidump -q to avoid message about ACPI information not being found.

Many arm64 systems use device trees instead of ACPI and acpidump is
expectected to fail on those systems.  And vmm(4) doesn't provide ACPI
information either.
ok deraadt@

src/etc/rc

@@ -1,4 +1,4 @@
-#	$OpenBSD: rc,v 1.529 2018/07/23 11:54:49 florian Exp $
+#	$OpenBSD: rc,v 1.530 2019/01/12 17:05:00 kettenis Exp $
 
 # System startup script run by init on autoboot or after single-user.
 # Output and error are redirected to console by init, and the console is the
@@ -507,7 +507,7 @@ fi
 
 # Store ACPI tables in /var/db/acpi to be used by sendbug(1).
 if [[ -x /usr/sbin/acpidump ]]; then
-	acpidump -o /var/db/acpi/
+	acpidump -q -o /var/db/acpi/
 fi
 
 if [[ $check_quotas == YES ]]; then