Driver is stable. Remove DEBUG definition from driver.

There are debug message in /var/log/messages if DEBUG is defined,
such as:
[MTK_V4L2] level=0 fops_vcodec_open(),170: decoder capability 0
[MTK_V4L2] level=0 fops_vcodec_open(),177: 16000000.vcodec decoder [0]
[MTK_V4L2] level=0 fops_vcodec_release(),200: [0] decoder
Signed-off-by: Minghsiu Tsai <minghsiu.tsai@mediatek.com>
Acked-by: Tiffany Lin <Tiffany.lin@mediatek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>