cmd/internal/obj/arm64: use obj.REG_NONE where appropriate
When referring to an unspecified register, use obj.REG_NONE rather than 0.
This has the same result but is more readable.
Change-Id: I56b541a3abc3c2c0e3ce1de21a624da0b21c485a
Reviewed-on: https://go-review.googlesource.com/c/go/+/461137 Reviewed-by: Eric Fang <eric.fang@arm.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au> Reviewed-by: Cherry Mui <cherryyz@google.com>