sys_util: fix new warning initializing Once
sys_util: fix new warning initializing Once

"warning: use of deprecated item 'std::sync::ONCE_INIT': the `new` function is now preferred"

Change-Id: I029611f2978d5baf3b0bc426ab2285e282708da0
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1715577
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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