[media] soc_camera: get the clock name by using macro: v4l2_clk_name_i2c()

Since v4l2_clk_name_i2c() is defined, reuse it.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>