kernfs: Clarify lockdep name for kn->count

The reference count in kernfs_node structure is treated like a rwsem by
using lockdep instrumentation code. The lockdep name, however, is still
"s_active" which is carried over from the old sysfs code. As s_active
is no longer the variable name, its use may confuse users on where the
lock is when it is reported by lockdep. So it is changed to "kn->count"
which is how this variable is normally referenced in kernfs code.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>