[media] s5k6aa: Make subdev name independent of the I2C slave address

Initialize the subdev name properly so it doesn't have an I2C
bus and slave address appended to it.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>