Revert "drivers: clk: zynqmp: update divider round rate logic"

This patch reverts the commit c249ef9d ("drivers: clk: zynqmp:
update divider round rate logic").

This is because that there has been a similar commit efe0d364
("drivers: clk: zynqmp: update divider round rate logic") which is
picked from SDK. This commit introduces some problem and the SDK patch
7e6654b5 ("drivers: clk: zynqmp: add hack to use old algorithm
for divider round rate") is to fix it. But when merging, the content of
the commit 7e6654b5 is missing. So we need to revert the commit
c249ef9d and bring the content of the commit 7e6654b5 back.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>