serial: 8250_dw: Simplify the ref clock rate setting procedure

serial: 8250_dw: Simplify the ref clock rate setting procedure

Really instead of twice checking the clk_round_rate() return value
we could do it once, and if it isn't error the clock rate can be changed.
By doing so we decrease a number of ret-value tests and remove a weird
goto-based construction implemented in the dw8250_set_termios() method.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200723003357.26897-3-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>