ColdFire: Fix UART baudrate formula

The formula "counter = (u32) (gd->bus_clk / gd->baudrate) / 32"
can generate the wrong divisor due to integer division truncation.
Round the calculated divisor value by adding 1/2 the baudrate
before dividing by the baudrate.

Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
Acked-by: Gerald Van Baren <vanbaren@cideas.com>