[PowerPC] Update alignment for ReuseLoadInfo in LowerFP_TO_INTForReuse

In LowerFP_TO_INTForReuse, when emitting `stfiwx`, alignment of 4 is
set for the `MachineMemOperand`, but RLI(ReuseLoadInfo)'s alignment is
not updated for following loads.

It's related to failed alignment check reported in
https://bugs.llvm.org/show_bug.cgi?id=45297

Differential Revision: https://reviews.llvm.org/D77624