[PATCH] powerpc: unified signature of timer_interrupt() between ppc32/ppc64

On ppc64 timer_interrupt() returned a value that was never used.  Changed
the ppc64 version of timer_interrupt() to no longer return a value so
that the signatures between ppc32 & ppc64 match.  This will simplify
future merging of arch/powerpc.

Signed-off-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>