01fips: trim off GRUB boot device from BOOT_IMAGE
    
    E.g. in RHCOS, the `BOOT_IMAGE` from the cmdline is:
    
    (hd0,gpt1)/ostree/rhcos-e493371e5ee8407889029ec979955a2b86fd7e3cae5a0591b9db1cd248d966e8/vmlinuz-4.18.0-146.el8.x86_64
    
    Which of course is a GRUB thing, not an actual pathname we'll be able to
    resolve. In fact, we can simply scrap it off from the variable. Our code
    is already able to handle both cases: whether the device refers to a
    separate boot partition, or just the root filesystem with a regular
    `/boot` directory.
    
    patch_name: 0056.patch
    present_in_specfile: true
    location_in_specfile: 56
    squash_commits: true