[media] media: s5p_mfc: remove s5p_mfc_get_node_type() function

s5p_mfc_get_node_type() relies on get_index() helper function, which in
turn relies on video_device index numbers assigned on driver
registration. All this code is not really needed, because there is
already access to respective video_device structures via common
s5p_mfc_dev structure. This fixes the issues introduced by patch
1056e438 ("v4l2-dev: Fix race condition
on __video_register_device"), which has been merged in v3.12-rc1.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: stable@vger.kernel.org
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>