media: v4l2: set the vfl_dir to default VFL_DIR_RX

The commit 49ed88a612 (media: at91sam9x5-video: modify
videodev "vfl_dir" policy) redefined the VFL_DIR macro.

Now 0 has no meaning for the vfl_dir feild. But many media
drivers use 0 as default. So we will convert 0 to default
VFL_DIR_RX value in __video_register_device() function.

This patch also modify the v4l2-dev.c according to
VFL_DIR_RX and VFL_DIR_TX values change.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Merge branch 'at91-3.10-trunk/v3.10_lcd+heo' into linux-3.10-at91