clk: vt8500: Fix device clock divisor calculations

When calculating device clock divisor values in set_rate and
round_rate, we do a simple integer divide. If parent_rate / rate
has a fraction, this is dropped which results in the device clock
being set too high.

This patch corrects the problem by adding 1 to the calculated
divisor if the division would have had a decimal result.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Mike Turquette <mturquette@linaro.org>