crimson/os/seastore/rbm: fix pass_admin to pass admin command to ioctl

The coroutine conversion accidentally passed nullptr to NVME_IOCTL_ADMIN_CMD,
so Identify always failed and SeaStore fell back to st_blksize (e.g. 128K),
breaking journal roll_start alignment on mkfs.

Signed-off-by: Aishwarya Mathuria <amathuri@redhat.com>