[PowerPC][Power10] Fix XXSPLI32DX not correctly exploiting specific cases

Some cases may be transformed into 32 bit splats before hitting the boolean statement, which may cause incorrect behaviour and provide XXSPLTI32DX with the incorrect values of splat. The condition was reversed so that the shortcut prevents this problem.

Differential Revision: https://reviews.llvm.org/D95634

(cherry picked from commit 2e470e03)