doxygen: fix duplicated defgroup for clock

Problen:
Duplicated definition of group_clk in clk.c and clk.h.

Solution:
Delete the definition in clk.c and keep only the definition
in clk.h.

Also change the name of group_clk to group_driver_clock to
conform to the naming convention of other driver groups.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>

components/drivers/clk/clk.c

@@ -14,10 +14,7 @@
 #include <rtdevice.h>
 
 /**
- * @defgroup    group_clk clk
- * @brief       clk driver api
- * @ingroup     group_device_driver
- * @addtogroup  group_clk
+ * @addtogroup group_driver_clock
  * @{
  */
 

components/drivers/include/drivers/clk.h

@@ -18,10 +18,13 @@
 #include <drivers/ofw.h>
 
 /**
- * @defgroup    group_clk clk
- * @brief       clk driver api
+ * @defgroup    group_driver_clock Clock
+ * @brief       Clock driver API
  * @ingroup     group_device_driver
- * @addtogroup  group_clk
+ */
+
+/**
+ * @addtogroup  group_driver_clock
  * @{
  */