staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic.

This patch makes locking in visorchannel_signalempty statically
deterministic.
As a result this patch fixes the sparse warning:
Context imbalance in 'visorchannel_signalempty' - different lock
contexts for basic block.

The logic of the locking code doesn't change but the layout of the
original code is "frowned upon"
according to mails on sparse context checking.
Refactoring removes the warning and makes the code more readable.

Signed-off-by: Cathal Mullaney <chuckleberryfinn@gmail.com>
Tested-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>