[RISC-V] Fix wrong CFA during stack probe

[RISC-V] Fix wrong CFA during stack probe

temp1 is used by the probe loop for the step size, but we need the final
address of the stack after the loop which resides in temp2.

	PR target/121121
	* config/riscv/riscv.cc (riscv_allocate_and_probe_stack_space):
	Use temp2 instead of temp1 for the CFA note.