Staging: unisys: channels: Cleanup sparse warnings

Clean up multiple sparse warnings mostly due to different address spaces
when accessing I/O memory.

Also, remove SignalRemoveAll(), SignalQueueHasOneElement(),
SignalQueueIsFull(), because they were never called.

Signed-off-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>