target-ppc: Fix use of uninitialized TCG variable in tlbiva

Silences a warning about possible unitialized use of t0.

Signed-off-by: Andreas Faerber <andreas.faerber@web.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5915 c046a42c-6fe2-441c-8c8c-71466251a162
