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.

modules.d/01fips/fips.sh

@@ -113,6 +113,10 @@ do_fips()
         do_rhevh_check /run/initramfs/live/isolinux/vmlinuz0 || return 1
     else
         BOOT_IMAGE="$(getarg BOOT_IMAGE)"
+
+        # Trim off any leading GRUB boot device (e.g. ($root) )
+        BOOT_IMAGE="$(echo "${BOOT_IMAGE}" | sed 's/^(.*)//')"
+
         BOOT_IMAGE_NAME="${BOOT_IMAGE##*/}"
         BOOT_IMAGE_PATH="${BOOT_IMAGE%${BOOT_IMAGE_NAME}}"