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>