chaps: fixup Linux build for new SecureBlob API

Commit 89f59bbe5df changed the interface for the SecureBlob class
and updated most of the Chaps code, but some of the Linux-specific
code was missed.

BUG=None
TEST=Chaps unit tests

Change-Id: Ib52743408caabc8a4e7c8dcf153073d22b286095
Reviewed-on: https://chromium-review.googlesource.com/263712
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: David Drysdale <drysdale@google.com>
Trybot-Ready: David Drysdale <drysdale@google.com>
Commit-Queue: Darren Krahn <dkrahn@chromium.org>
2 files changed