mei: make me client counters less error prone

1. u8 counters are prone to hard to detect overflow:
 make them unsigned long to match bit_ functions argument type

2. don't check me_clients_num for negativity, it is unsigned.

3. init all the me client counters from one place

Cc:  <stable@vger.kernel.org> # 3.9+
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>