gpu: nvgpu: Clear invalid method

Invalid method needs to be cleared in gm20b to prevent getting same
interrupt again.

Change-Id: I4d83d1a27e5c711b5d82b95552be84d5f16a13e0
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/500286

drivers/gpu/nvgpu/gk20a/fifo_gk20a.c

@@ -1482,6 +1482,7 @@ static u32 gk20a_fifo_handle_pbdma_intr(struct device *dev,
 				    pbdma_intr_0);
 		}
 
+		gk20a_writel(g, pbdma_method0_r(pbdma_id), 0);
 		gk20a_writel(g, pbdma_intr_0_r(pbdma_id), pbdma_intr_0);
 	}