ipa: rkisp1: awb: Freeze AWB when means are too small

When the RGB means are too small, gains and color temperature can't be
meaningfully calculated. Freeze the AWB in that case, using the
previously calculated values.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/ipa/rkisp1/ipa_context.cpp

@@ -156,6 +156,9 @@ namespace libcamera::ipa::rkisp1 {
  * \var IPAActiveState::awb.gains.automatic.blue
  * \brief Automatic white balance gain for B channel
  *
+ * \var IPAActiveState::awb.temperatureK
+ * \brief Estimated color temperature
+ *
  * \var IPAActiveState::awb.autoEnabled
  * \brief Whether the Auto White Balance algorithm is enabled
  */