drm: arcpgu: Fix module unload

At module unload we are expecting a struct drm_device but at
probing we are not setting it right. Fix this and correct the
arcpgu module unload.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Fixes: 0c4250e7b15e ("drm: Add support of ARC PGU display controller")
Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

drivers/gpu/drm/arc/arcpgu_drv.c

@@ -120,7 +120,7 @@ static int arcpgu_load(struct drm_device *drm)
 		return -ENODEV;
 	}
 
-	platform_set_drvdata(pdev, arcpgu);
+	platform_set_drvdata(pdev, drm);
 	return 0;
 }