[media] s5p-fimc: Don't create multiple active links to same sink entity

The driver is supposed to create active media link from sensor N
(or its corresponding s5p-mipi-csis entity) to FIMC.N by default.
Instead s5p-mipi-csis.N entity gets  always connected by a default
active link to FIMC.N, regardless of there are parallel bus sensor
entities already connected to FIMC.N. Correct this.

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>