runtime: remove redundant explicit deref in trace.go

runtime: remove redundant explicit deref in trace.go

Replaces legacy Go syntax for pointer struct member access
with more modern auto-deref alternative.

Found using https://go-critic.github.io/overview#underef-ref

Change-Id: I71a3c424126c4ff5d89f9e4bacb6cc01c6fa2ddf
Reviewed-on: https://go-review.googlesource.com/122895
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>