m68knommu: fix fec driver interrupt races

The FEC driver has a common interrupt handler for all interrupt event
types. It is raised on a number of distinct interrupt vectors.
This handler can't be re-entered while processing an interrupt, so
make sure all requested vectors are flagged as IRQF_DISABLED.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>