dm: avoid NULL dereference in add_item()

acpi_add_other_item() passes dev = NULL. Instead of dev->name write the
string "other" to the debug log:

    ACPI: Writing ACPI tables at 1fd3000
    0base: writing table '<NULL>'
    * other: Added type 3, 0000000011fd4000, size 240
    1facs: writing table 'FACS'
    * other: Added type 3, 0000000011fd4240, size 40
    5csrt: writing table 'CSRT'
    * other: Added type 3, 0000000011fd4280, size 30

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/acpi.c b/drivers/core/acpi.c
index 0df58db..8457733 100644
--- a/drivers/core/acpi.c
+++ b/drivers/core/acpi.c
@@ -159,8 +159,8 @@
 		memcpy(item->buf, start, item->size);
 	}
 	item_count++;
-	log_debug("* %s: Added type %d, %p, size %x\n", dev->name, type, start,
-		  item->size);
+	log_debug("* %s: Added type %d, %p, size %x\n",
+		  dev ? dev->name : "other", type, start, item->size);
 
 	return 0;
 }