serial: 8250_pericom: Use serial_dl_write() instead of open coded

serial: 8250_pericom: Use serial_dl_write() instead of open coded

It's better to stick with standard API to write and read DL value
when the hardware is compatible with it. In case any quirks are
needed it may be easily added in one place rather than modifying
code here and there.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211122133512.8947-4-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>