tools/cargo-doc: exclude crosvm-fuzz
tools/cargo-doc: exclude crosvm-fuzz

crosvm-fuzz only contains fuzzer binaries, which don't have any
documentable items and clutter up the list of crates.

BUG=None
TEST=tools/cargo-doc

Change-Id: I0a8a5a61977643920d66a0f2662a1050a66192a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3630425
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>

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