staging: bcm2835-camera: Correct V4L2_CID_COLORFX_CBCR behaviour

With V4L2_CID_COLORFX_CBCR calling ctrl_set_colfx it was incorrectly
assigning the colour values to the enable field of dev->colourfx
instead of the u and v fields.

Correct the assignments.

Reported as a Coverity issue
Detected by CoverityScan CID#1419711 ("Unused value")

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>