cmd/internal/obj: adjust (*Link).AllPos comment in inl.go
cmd/internal/obj: adjust (*Link).AllPos comment in inl.go

AllPos truncates and overwrites its slice-storage input instead
of appending.  This makes that clear.

Change-Id: I81653ff49a4a7d14fe9446fd6620943f3b20bbd3
Reviewed-on: https://go-review.googlesource.com/c/go/+/449478
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@google.com>
Run-TryBot: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go