staging: unisys: Don't check for null before getting driver device.

The macro to convert to the driver object was giving a checkpatch warning
when it ateempted to check for a null driver. It would return NULL if it
found it, but only one location was checking to see if it was NULL.

Remove the check in the MACRO and do it prior to calling the macro if
required.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>