linux: remove unnecessary usize casts
linux: remove unnecessary usize casts

The expressions that are being converted to usize are already naturally
usize without the casts.

BUG=None
TEST=build_test

Change-Id: Ifb8553e20a3d57cb5edb38dcfcd423edf12a1a28
Signed-off-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1396483
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm