When building serial_base as a module, modpost fails with the following
error message:

  ERROR: modpost: "match_devname_and_update_preferred_console"
  [drivers/tty/serial/serial_base.ko] undefined!

Export the symbol to allow using it from modules.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409071312.qlwtTOS1-lkp@intel.com/
Fixes: 12c91cec ("serial: core: Add serial_base_match_and_update_preferred_console()")
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Link: https://lore.kernel.org/r/20240909075652.747370-1-liaoyu15@huawei.comSigned-off-by: Petr Mladek <pmladek@suse.com>