[AMDGPU] Visit all PHIs in each call to optimizeLiveType (#147522)
Make the Visited set a local variable, otherwise we can reject a PHI
(those that do not have a zeroinitializer constant) but mark it as
visited,
and the rest of the function thinks the PHI is ok when it isn't.
This is a bit crude but it's the only fix that consistently worked in my
testing.
Fixes SWDEV-541767