aarch64: Fix typo in aarch64-ldp-fusion.cc:combine_reg_notes [PR114936]

aarch64: Fix typo in aarch64-ldp-fusion.cc:combine_reg_notes [PR114936]

This fixes a typo in combine_reg_notes in the load/store pair fusion
pass.  As it stands, the calls to filter_notes store any
REG_FRAME_RELATED_EXPR to fr_expr with the following association:

 - i2 -> fr_expr[0]
 - i1 -> fr_expr[1]

but then the checks inside the following if statement expect the
opposite (more natural) association, i.e.:

 - i2 -> fr_expr[1]
 - i1 -> fr_expr[0]

this patch fixes the oversight by swapping the fr_expr indices in the
calls to filter_notes.

In hindsight it would probably have been less confusing / error-prone to
have combine_reg_notes take an array of two insns, then we wouldn't have
to mix 1-based and 0-based indexing as well as remembering to call
filter_notes in reverse program order.  This however is a minimal fix
for backporting purposes.

gcc/ChangeLog:

	PR target/114936
	* config/aarch64/aarch64-ldp-fusion.cc (combine_reg_notes):
	Ensure insn iN has its REG_FRAME_RELATED_EXPR (if any) stored in
	FR_EXPR[N-1], thus matching the correspondence expected by the
	copy_rtx calls.