powerpc: Fix STAB initialization

commit 13938117a57f88a22f0df9722a5db7271fda85cd upstream.

Commit f5339277eb8d3aed37f12a27988366f68ab68930 accidentally removed
more than just iSeries bits and took out the call to stab_initialize()
thus breaking support for POWER3 processors.

Put it back. (Yes, nobody noticed until now ...)

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>