powerpc/booke: don't reinitialize time base

For some reason long ago I decided that we should zero out the time base
when we calibrate the decrementer.  The problem is that this can be
harmful in SMP systems where the firmware has already synchronized the
time bases on the various cores.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

diff --cc arch/powerpc/kernel/time.c
Simple merge