media: imx274: remove unused data from struct imx274_frmfmt

struct imx274_frmfmt is instantiated only in the imx274_formats[]
array, where imx274_formats[N].mode always equals N (via enum
imx274_mode).  So .mode carries no information, and unsurprisingly it
is never used.

mbus_code is never used because the 12 bit modes are not implemented.

The colorspace member is also never used, which is normal since the
imx274 sensor can output only one colorspace.

Let's get rid of all of them.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>