cmd/internal/obj/riscv: correct CALL reloc symbol handling

Move the CALL reloc symbol back to p.From.Sym, rather than p.To.Sym - while
p.To.Sym is the correct final location, the call to lowerJALR flips the p.To
and p.From addresses (and proves that this form of obj.Prog rewriting is not
a good idea).

Updates #27532

Change-Id: Iaf9fa24b05bda32b963f8d243401c6cd82c1355c
Reviewed-on: https://go-review.googlesource.com/c/go/+/212759


Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>