This patch fixes the a compile error with CONFIG_SYSFS=n

Configfs is creating, as a matter of policy, the /sys/kernel/config
mountpoint.  This means it requires CONFIG_SYSFS.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>