media: i2c: imx477: Do not unconditionally adjust hblank and vblank limits

On a mode change, only call imx477_set_framing_limits() to adjust the hblank
and vblank limits if the new mode is different from the existing mode. This
preserves any manual control values the user might have set.

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