m68knommu: fix mis-named variable int set_irq_chip loop

Compiling for 68360 targets gives:

  CC      arch/m68knommu/platform/68360/ints.o
arch/m68knommu/platform/68360/ints.c: In function ‘init_IRQ’:
arch/m68knommu/platform/68360/ints.c:135:16: error: ‘irq’ undeclared (first use in this function)
arch/m68knommu/platform/68360/ints.c:135:16: note: each undeclared identifier is reported only once for each function it appears in

Fix variable name used.

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