aarch64: Re-parent trailing nondebug base reg uses [PR113089]

While working on PR113089, I realised we where missing code to re-parent
trailing nondebug uses of the base register in the case of cancelling
writeback in the load/store pair pass.  This patch fixes that.

gcc/ChangeLog:

	PR target/113089
	* config/aarch64/aarch64-ldp-fusion.cc (ldp_bb_info::fuse_pair):
	Update trailing nondebug uses of the base register in the case
	of cancelling writeback.