serial: 8250_exar: Consolidate callback assignments in default_setup()

For better maintenance consolidate port callbacks in default_setup().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20190805142535.21948-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>