pair-fusion: Tweak wording in dump message [PR118320]

As discussed in
https://gcc.gnu.org/pipermail/gcc-patches/2025-February/675978.html
this tweaks the dump messasge added with the fix for PR118320 since it doesn't
just apply to load pairs.

gcc/ChangeLog:

	PR rtl-optimization/118320
	* pair-fusion.cc (pair_fusion_bb_info::fuse_pair): Tweak wording in dump
	message when punting on invalid use arrays.