m68knommu: fix ColdFire 5272 serial baud rates in mcf.c

I noticed (the hard way) that the mcf.c driver doesn't support the fractional precision register on the MCF5272.  This makes the console dicey at 115200 baud and a system clock of 66.0 MHz.  On the other hand, if your hardware is running at 66.666 MHz, it probably isn't a problem.

Patch submitted by John Adamson <jadamson@allen-organ.com>

Signed-off-by: Greg Ungerer <gerg@uclinux.org>