media: i2c: imx477: Remove internal v4l2_mbus_framefmt from the state

The only field in this struct that is used is the format code, so
replace the struct with this single field.

Save the format code in imx477_set_pad_format() when setting up a new
mode so that imx477_get_pad_format() performs the right lookup.
Otherwise, this caused a bug where the mode lookup occurred on the
12-bit table rather than the 10-bit table.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>