staging: unisys: Fix incorrect unisys MAINTAINERS pattern

Fix stale path to documentation in MAINTAINERS file.
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Acked-by: David Kershner <david.kershne@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/MAINTAINERS

 Unisys s-Par drivers
 M:	David Kershner <sparmaintainer@unisys.com>
 S:	Maintained
-F:	Documentation/s-Par/overview.txt
+F:	drivers/staging/unisys/Documentation/overview.txt
 F:	drivers/staging/unisys/