staging: unisys: visorchannel: Describe spinlocks in VISORCHANNEL_Tag struct

Add comments indicating the requirements and use of the insert_lock and
remove_lock in the VISORCHANNEL_Tag structure.

Signed-off-by: Bryan Thompson <bryan.thompson@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>