Input: serio_raw - fix memory leak when closing char device

Apparently we never freed memory allocated when users open our char
devices nor removed old users from the list of connected clients.

Also unregister misc device immediately upon disconnecting the port
instead of waiting until last user drops off (refcounting in misc
device code will make sure needed pieces stay around while they
are needed) and make sure we are not holing holding serio_raw_mutex
when registering/unregistering misc device. This should fix potential
deadlock between serio_raw and misc device code uncovered by lockdep
and reported by Thomas Tuttle.

Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>