serial: 8250_dw: Revert "Improve clock rate setting"

The commit

  de9e33bd ("serial: 8250_dw: Improve clock rate setting")

obviously tries to cure symptoms, and not a root cause.

The root cause is the non-flexible rate calculation inside the
corresponding clock driver. What we need is to provide maximum UART
divisor value to the clock driver to allow it do the job transparently
to the caller.

Since from the initial commit message I have got no clue which clock
driver actually needs to be amended, I leave this exercise to the people
who know better the case.

Moreover, it seems [1] the fix introduced a regression. And possible
even one more [2].

Taking above, revert the commit de9e33bd for now.

[1]: https://www.spinics.net/lists/linux-serial/msg28872.html
[2]: https://github.com/Dunedan/mbp-2016-linux/issues/29#issuecomment-357583782



Fixes: de9e33bd ("serial: 8250_dw: Improve clock rate setting")
Cc: stable <stable@vger.kernel.org> # 4.15
Cc: Ed Blake <ed.blake@sondrel.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>