[RISC-V][PR target/127318] Attach DEF_CFA to correct insn

As is noted in the PR, the REG_CFA_DEF_DFA note is wrong for the testcase,
while I get meaningfully different CFA note locations than the author, it is
clear that the note is getting attached to the wrong insn.

The CFA_DEF_CFA note should get attached to the insn that copies from the stack
pointer into the temporary.  The RISC-V port tried to do that, but appears to
have just gotten the logic wrong.  The net is the CFA_DEF_CFA note got attached
to the insn before the stack pointer copy.  Worse yet the insn with the note
could move around relative to the stack pointer for scheduling purposes.

The fix is trivial.  We just need to attach the note to the sp->temp copy.
Given this doesn't affect code generation, but is a correctness issue, I will
go ahead and backport it immediately rather than waiting for the usual simmer
on the trunk.

Bootstrapped and regression tested on the K3 and c920.  Also tested for the
riscv32-elf and riscv64-elf platforms.

	PR target/127318
gcc/
	* config/riscv/riscv.cc (riscv_v_adjust_scalable_frame): Attach
	REG_CFA_DEF_CFA note to the copy from the stack pointer.