kernel_loader: Fix clippy warnings.
kernel_loader: Fix clippy warnings.

Should use &<vec> instead of <vec>.iter() in a for loop.
cmdline returns a size that can't be negative.

Change-Id: I5f0ee3584d8890ac26feaadb99360b2d23f67d70
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/515604
Commit-Ready: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Tested-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

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