sparseirq, powerpc/cell: fix unused variable warning in interrupt.c

This new compiler warning:

   arch/powerpc/platforms/cell/interrupt.c: In function 'handle_iic_irq':
   arch/powerpc/platforms/cell/interrupt.c:240: warning: unused variable 'cpu'

Triggers because the local variable 'cpu' became unused due to commit:

   dee4102a

: sparseirq: use kstat_irqs_cpu instead

Remove the variable.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: ppc-dev <linuxppc-dev@ozlabs.org>
LKML-Reference: <20090316185256.4a160374.sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>