staging: unisys: rework signal remove/insert to avoid sparse lock warnings

Avoids the following warnings from sparse:
visorchannel_funcs.c:457:9: warning:
 context imbalance in 'visorchannel_signalremove' - different lock contexts for basic block
visorchannel_funcs.c:512:9: warning:
 context imbalance in 'visorchannel_signalinsert' - different lock contexts for basic

These warnings are false positives. Sparse can't track conditional contexts. The change
puts the lock/unlock into the same context by splitting the insert/remove functions each
into a wrapper function that does locking if necessary and an inner function that does the
insert/remove operation.

Signed-off-by: Zachary Warren <conflatulence@gmail.com>
Acked-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>