security: clarify cap_inode_getsecctx description

Make it clear that cap_inode_getsecctx shouldn't return success without
filling in the context data.
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

include/linux/security.h

@@ -1392,7 +1392,8 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  * 	@ctxlen contains the length of @ctx.
  *
  * @inode_getsecctx:
- *	Returns a string containing all relevant security context information
+ *	On success, returns 0 and fills out @ctx and @ctxlen with the security
+ *	context for the given @inode.
  *
  * 	@inode we wish to get the security context of.
  *	@ctx is a pointer in which to place the allocated security context.