[media] em28xx: make em28xx_free_v4l2 static()

Changeset 95d2608b88 created this function, but declared it as
global, by mistake.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --cc drivers/media/usb/em28xx/em28xx-video.c
Simple merge