Currently a mixture of cbl-mariner and mariner is used when creating the
mariner initrd. The kata-static tarball has mariner in the name, but the
jenkins url uses cbl-mariner. This breaks cache usage.
Use mariner as the target name throughout the build, so that caching works.
Fixes: #7292
Signed-off-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>