serial: 8250_exar: Remove duplicate assignment

UPF_EXAR_EFR is set globally for each port enumerated by the driver.
Thus, no need to repeat this in individual ->setup() hook.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>