media: imx-jpeg: Don't fill the description field in struct v4l2_fmtdesc

The core will fill this in v4l_fill_fmtdesc(),
ensuring consistent format description names.

Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>