dm: define LOG_CATEGORY for all uclass

Define LOG_CATEGORY for all uclass to allow filtering with
log command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/ram/ram-uclass.c b/drivers/ram/ram-uclass.c
index f4d387f..4e21240 100644
--- a/drivers/ram/ram-uclass.c
+++ b/drivers/ram/ram-uclass.c
@@ -4,6 +4,8 @@
  * Written by Simon Glass <sjg@chromium.org>
  */
 
+#define LOG_CATEGORY UCLASS_RAM
+
 #include <common.h>
 #include <ram.h>
 #include <dm.h>