staging: unisys: remove typedef SIGNAL_QUEUE_HEADER

Get rid of the typedef for SIGNAL_QUEUE_HEADER and use struct
signal_queue_header directly instead. Fix all references to the typedef
to use the struct.

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