dm table: fix "nvme" test

The strncmp function should compare 4 bytes.

Fixes: 22c11858e8002 ("dm: introduce DM_TYPE_NVME_BIO_BASED")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
1 file changed