serial: 8250: pericom_do_set_divisor can be static

Fixes: 6bf4e42f

 ("serial: 8250: Add support for higher baud rates to Pericom chips")
Signed-off-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>