dmaengine: stm32-dmamux: Fix a NULL vs IS_ERR() check in probe

devm_ioremap_resource() doesn't return NULL, it returns error pointers.

Fixes: df7e762db5f6 ("dmaengine: Add STM32 DMAMUX driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/stm32-dmamux.c

@@ -257,8 +257,8 @@ static int stm32_dmamux_probe(struct platform_device *pdev)
 		return -ENODEV;
 
 	iomem = devm_ioremap_resource(&pdev->dev, res);
-	if (!iomem)
-		return -ENOMEM;
+	if (IS_ERR(iomem))
+		return PTR_ERR(iomem);
 
 	spin_lock_init(&stm32_dmamux->lock);