dm: Use uclass_first_device_err() where it is useful

Use this new function in places where it simplifies the code.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/nios2/cpu/cpu.c b/arch/nios2/cpu/cpu.c
index be7f99c..4f0f8fc 100644
--- a/arch/nios2/cpu/cpu.c
+++ b/arch/nios2/cpu/cpu.c
@@ -63,11 +63,9 @@
 	struct udevice *dev;
 	int ret;
 
-	ret = uclass_first_device(UCLASS_CPU, &dev);
+	ret = uclass_first_device_err(UCLASS_CPU, &dev);
 	if (ret)
 		return ret;
-	if (!dev)
-		return -ENODEV;
 
 	gd->ram_size = CONFIG_SYS_SDRAM_SIZE;
 #ifndef CONFIG_ROM_STUBS