media: staging/imx: fix complete handler

The complete handler walks all entities, expecting to find an imx
subdevice for each and every entity.

However, camera drivers such as smiapp can themselves contain multiple
entities, for which there will not be an imx subdevice.  This causes
imx_media_find_subdev_by_sd() to fail, making the imx capture system
unusable with such cameras.

Work around this by killing the error entirely, thereby allowing
the imx capture to be used with such cameras.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>