logfs: fix compile failure

When CONFIG_BLOCK is not enabled:

fs/logfs/super.c:142: error: implicit declaration of function 'bdev_get_queue'
fs/logfs/super.c:142: error: invalid type argument of '->' (have 'int')

Found by Randy Dunlap <randy.dunlap@oracle.com>

Signed-off-by: Joern Engel <joern@logfs.org>