serial: mvebu-uart: fix calculation of clock divisor

The clock divisor should be rounded to the closest value.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: 68a0db1d ("serial: mvebu-uart: add function to change baudrate")
Cc: stable@vger.kernel.org # 0e4cf69e ("serial: mvebu-uart: clarify the baud rate derivation")
Link: https://lore.kernel.org/r/20210624224909.6350-2-pali@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>