serial: max310x: Fix build warning

config: x86_64-randconfig-x006 (attached as .config)

All warnings:

 drivers/tty/serial/max310x.c: In function 'max310x_probe':
>> drivers/tty/serial/max310x.c:1240:1: warning: label 'out_uart' defined but not used [-Wunused-label]

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>