dmaengine: stm32: dmamux: fix device leak on route allocation

Make sure to drop the reference taken when looking up the DMA mux
platform device during route allocation.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

Fixes: df7e762 ("dmaengine: Add STM32 DMAMUX driver")
Cc: stable@vger.kernel.org	# 4.15
Cc: Pierre-Yves MORDRET <pierre-yves.mordret@foss.st.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://patch.msgid.link/20251117161258.10679-11-johan@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: jhovold

drivers/dma/stm32/stm32-dmamux.c

@@ -90,23 +90,25 @@ static void *stm32_dmamux_route_allocate(struct of_phandle_args *dma_spec,
 	struct stm32_dmamux_data *dmamux = platform_get_drvdata(pdev);
 	struct stm32_dmamux *mux;
 	u32 i, min, max;
-	int ret;
+	int ret = -EINVAL;
 	unsigned long flags;
 
 	if (dma_spec->args_count != 3) {
 		dev_err(&pdev->dev, "invalid number of dma mux args\n");
-		return ERR_PTR(-EINVAL);
+		goto err_put_pdev;
 	}
 
 	if (dma_spec->args[0] > dmamux->dmamux_requests) {
 		dev_err(&pdev->dev, "invalid mux request number: %d\n",
 			dma_spec->args[0]);
-		return ERR_PTR(-EINVAL);
+		goto err_put_pdev;
 	}
 
 	mux = kzalloc(sizeof(*mux), GFP_KERNEL);
-	if (!mux)
-		return ERR_PTR(-ENOMEM);
+	if (!mux) {
+		ret = -ENOMEM;
+		goto err_put_pdev;
+	}
 
 	spin_lock_irqsave(&dmamux->lock, flags);
 	mux->chan_id = find_first_zero_bit(dmamux->dma_inuse,
@@ -133,7 +135,6 @@ static void *stm32_dmamux_route_allocate(struct of_phandle_args *dma_spec,
 	dma_spec->np = of_parse_phandle(ofdma->of_node, "dma-masters", i - 1);
 	if (!dma_spec->np) {
 		dev_err(&pdev->dev, "can't get dma master\n");
-		ret = -EINVAL;
 		goto error;
 	}
 
@@ -160,13 +161,18 @@ static void *stm32_dmamux_route_allocate(struct of_phandle_args *dma_spec,
 	dev_dbg(&pdev->dev, "Mapping DMAMUX(%u) to DMA%u(%u)\n",
 		mux->request, mux->master, mux->chan_id);
 
+	put_device(&pdev->dev);
+
 	return mux;
 
 error:
 	clear_bit(mux->chan_id, dmamux->dma_inuse);
 
 error_chan_id:
 	kfree(mux);
+err_put_pdev:
+	put_device(&pdev->dev);
+
 	return ERR_PTR(ret);
 }