m68knommu: fix 5407 ColdFire UART vector setup

There is a couple of problems with the UART vector setup for the 5307
ColdFire UART. The ICR register access should be 8bit, not 32bit. The
address of the UIVR register is wrong, it needs to be offset into the
MBAR register region. Fix these.

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