serial: 8250_dw: Pass the same rate to the clk round and set rate methods

Indeed according to the clk API if clk_round_rate() has successfully
accepted a rate, then in order setup the clock with value returned by the
clk_round_rate() the clk_set_rate() method must be called with the
original rate value.

Suggested-by: Russell King <linux@armlinux.org.uk>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>

Link: https://lore.kernel.org/r/20200723003357.26897-4-Sergey.Semin@baikalelectronics.ru


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