[media] vivid: comment the unused g_edid/s_edid functions

[media] vivid: comment the unused g_edid/s_edid functions

Those non-static functions aren't used anywhere yet. Comment them
while they're unused.

Solves the following warnings:

drivers/media/platform/vivid/vivid-vid-out.c:1120:5: warning: no previous prototype for 'vivid_vid_out_g_edid' [-Wmissing-prototypes]
 int vivid_vid_out_g_edid(struct file *file, void *_fh,
     ^
drivers/media/platform/vivid/vivid-vid-out.c:1152:5: warning: no previous prototype for 'vivid_vid_out_s_edid' [-Wmissing-prototypes]
 int vivid_vid_out_s_edid(struct file *file, void *_fh,
     ^

Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>