USB: serial: only process sysrq when enabled

Do not set the sysrq timestamp unless CONFIG_MAGIC_SYSRQ is enabled to
avoid unnecessary per-character processing for consoles.
Reviewed-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/generic.c

@@ -594,7 +594,7 @@ EXPORT_SYMBOL_GPL(usb_serial_handle_sysrq_char);
 
 int usb_serial_handle_break(struct usb_serial_port *port)
 {
-	if (!port->port.console)
+	if (!port->port.console || !IS_ENABLED(CONFIG_MAGIC_SYSRQ))
 		return 0;
 
 	if (!port->sysrq) {