OMAPDSS: fix dss_fck clock rate rounding

OMAPDSS: fix dss_fck clock rate rounding

DSS func clock is calculated with prate / div * m. However, the current
omapdss code calculates it with prate * m / div, which yields a slightly
different result when there's a remainder. For example, 432000000 / 14 *
2 = 61714284, but 432000000 * 2 / 14 = 61714285.

In addition to that, the clock framework wants the clock rate given with
clk_set_rate to be higher than the actual (truncated) end result. So, if
prate is 432000000, and div is 14, the real result is 30857142.8571...
We need to call clk_set_rate with 30857143, which gives us a clock of
30857142. That's why we need to use DIV_ROUND_UP() when calling
clk_set_rate.

This patch fixes the clock calculation.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>