drm/nouveau/fifo/g84-: ack non-stall interrupt before handling it

Closes a very unlikely race that can occur if another NonStallInterrupt
method passes between checking fences and acking the previous interrupt.

With this change, the interrupt will re-fire under such conditions.

Tested-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/core/engine/fifo/nvc0.c b/drivers/gpu/drm/nouveau/core/engine/fifo/nvc0.c
index 1fe1f8f..074d434 100644
--- a/drivers/gpu/drm/nouveau/core/engine/fifo/nvc0.c
+++ b/drivers/gpu/drm/nouveau/core/engine/fifo/nvc0.c
@@ -740,6 +740,8 @@
 	u32 inte = nv_rd32(priv, 0x002628);
 	u32 unkn;
 
+	nv_wr32(priv, 0x0025a8 + (engn * 0x04), intr);
+
 	for (unkn = 0; unkn < 8; unkn++) {
 		u32 ints = (intr >> (unkn * 0x04)) & inte;
 		if (ints & 0x1) {
@@ -751,8 +753,6 @@
 			nv_mask(priv, 0x002628, ints, 0);
 		}
 	}
-
-	nv_wr32(priv, 0x0025a8 + (engn * 0x04), intr);
 }
 
 static void