sys_util: do not treat EINTR as negative in handle_eintr
sys_util: do not treat EINTR as negative in handle_eintr

System error codes are positive, we should not try to use the negative
(kernel) form when working with it.

TEST=cargo test --features plugin; cargo test -p sys_util
BUG=None

Change-Id: I8dea773e6148d1814ca0ea5019d5fb7824dc80ac
Signed-off-by: Dmitry Torokhov <10a8c465cefc9bdd6c925e26964d23c90f1141cc@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/940611
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

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