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/spmi/spmi-uclass.c b/drivers/spmi/spmi-uclass.c
index ff09873..9d9f46a 100644
--- a/drivers/spmi/spmi-uclass.c
+++ b/drivers/spmi/spmi-uclass.c
@@ -5,6 +5,8 @@
  * (C) Copyright 2015 Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
  */
 
+#define LOG_CATEGORY UCLASS_SPMI
+
 #include <common.h>
 #include <dm.h>
 #include <errno.h>