intra_dc_precision is a 2-bit integer [1]
allow use of all valid options, 8 - 11 bits precision

[1] ISO/IEC 13818-2 Table 6-13

Fixes: c27bb30e ("media: v4l: Add definitions for MPEG-2 slice format and metadata")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>