vfio-mdev: Fix mtty sample driver building

This sample driver was originally under Documentation/ and was moved
to samples, but build support was never adjusted for the new location.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
diff --git a/samples/Makefile b/samples/Makefile
index e17d66d..86a137e 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -2,4 +2,5 @@
 
 obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ trace_events/ livepatch/ \
 			   hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \
-			   configfs/ connector/ v4l/ trace_printk/ blackfin/
+			   configfs/ connector/ v4l/ trace_printk/ blackfin/ \
+			   vfio-mdev/