power: regulator: stm32-verfbuf: define LOG_CATEGORY

Define LOG_CATEGORY to allow filtering with log command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/power/regulator/stm32-vrefbuf.c b/drivers/power/regulator/stm32-vrefbuf.c
index c2c5770..c37998a 100644
--- a/drivers/power/regulator/stm32-vrefbuf.c
+++ b/drivers/power/regulator/stm32-vrefbuf.c
@@ -6,6 +6,8 @@
  * Originally based on the Linux kernel v4.16 drivers/regulator/stm32-vrefbuf.c
  */
 
+#define LOG_CATEGORY UCLASS_REGULATOR
+
 #include <common.h>
 #include <clk.h>
 #include <dm.h>