unix: simplify error handling in *listxattr on FreeBSD
unix: simplify error handling in *listxattr on FreeBSD

The var e error declaration is shadowed inside the for loop, so the
outer e always stays nil. Also, there is no need to reset the inner e in
case of EPERM, as it is reset by ExattrList* on the next iteration
anyhow.

Change-Id: Ib395e34b5a390a5d37bee334c44f6f87d3add2a0
Reviewed-on: https://go-review.googlesource.com/85295
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

multiplay/golang-sys,golang/sys,multiplay/golang-sys,multiplay/golang-sys,multiplay/golang-sys,golang/sys,golang/sys