Use span-based file API in inspect_utils_linux.cc

No functionality change.

Bug: 435317390
Change-Id: I133a61d17ea1aa86874b77f67ce30452965dc63e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7212363
Commit-Queue: Lei Zhang <thestig@chromium.org>
Auto-Submit: Jan Keitel <jkeitel@google.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1552946}
NOKEYCHECK=True
GitOrigin-RevId: 4f69e2c14be55c4f603bd87996aa1ee6319d4234