Make all v4l2-clk's clock name use V4L2_CLK_NAME_SIZE definition.

In future, if the string is increased we just need to change the
V4L2_CLK_NAME_SIZE once.
Signed-off-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>