[PATCH] debugfs: add header file

debugfs needs include/linux/kobject.h for <kernel_subsys>.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>