firmware: dmi: handle missing DMI data gracefully

Currently, when booting a kernel with DMI support on a platform that has
no DMI tables, the following output is emitted into the kernel log:

  [    0.128818] DMI not present or invalid.
  ...
  [    1.306659] dmi: Firmware registration failed.
  ...
  [    2.908681] dmi-sysfs: dmi entry is absent.

The first one is a pr_info(), but the subsequent ones are pr_err()s that
complain about a condition that is not really an error to begin with.

So let's clean this up, and give up silently if dma_available is not set.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Hundebøll <mnhu@prevas.dk>
Signed-off-by: Jean Delvare <jdelvare@suse.de>

drivers/firmware/dmi-sysfs.c

@@ -652,7 +652,7 @@ static int __init dmi_sysfs_init(void)
 	int val;
 
 	if (!dmi_kobj) {
-		pr_err("dmi-sysfs: dmi entry is absent.\n");
+		pr_debug("dmi-sysfs: dmi entry is absent.\n");
 		error = -ENODATA;
 		goto err;
 	}

drivers/firmware/dmi_scan.c

@@ -704,10 +704,8 @@ static int __init dmi_init(void)
 	u8 *dmi_table;
 	int ret = -ENOMEM;
 
-	if (!dmi_available) {
-		ret = -ENODATA;
-		goto err;
-	}
+	if (!dmi_available)
+		return 0;
 
 	/*
 	 * Set up dmi directory at /sys/firmware/dmi. This entry should stay