LSM: lsm_hooks.h - fix missing colon in docstring

Apparently without it it is incorrect syntax and causes a warning about
undocumented struct field.

Fixes: b230d5ab ("LSM: add new hook for kernfs node initialization")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

include/linux/lsm_hooks.h

@@ -447,7 +447,7 @@
  *
  * Security hooks for kernfs node operations
  *
- * @kernfs_init_security
+ * @kernfs_init_security:
  *	Initialize the security context of a newly created kernfs node based
  *	on its own and its parent's attributes.
  *