scripts/coverity-scan/COMPONENTS.md: Add loongarch component

Add the component regex for the new loongarch target.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20220718142310.16013-2-peter.maydell@linaro.org