[media] V4L2: add a v4l2-clk helper macro to produce an I2C device ID

To obtain a clock reference consumers supply their device object to the
V4L2 clock framework. The latter then uses the consumer device name to
find a matching clock. For that to work V4L2 clock providers have to
provide the same device name, when registering clocks. This patch adds
a helper macro to generate a suitable device name for I2C devices.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

include/media/v4l2-clk.h

@@ -65,4 +65,7 @@ static inline struct v4l2_clk *v4l2_clk_register_fixed(const char *dev_id,
 	return __v4l2_clk_register_fixed(dev_id, id, rate, THIS_MODULE);
 }
 
+#define v4l2_clk_name_i2c(name, size, adap, client) snprintf(name, size, \
+			  "%d-%04x", adap, client)
+
 #endif