media: imx-pxp: fix duplicated if condition

Fix a copy&paste error to make RGB -> BT.2020 YUV conversion actually
selectable. Fixes the following warning:

  drivers/media/platform/imx-pxp.c:683:24: warning: duplicated ‘if’ condition [-Wduplicated-cond]

Fixes: 51abcf7f ("media: imx-pxp: add i.MX Pixel Pipeline driver")

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>