soc-camera: return -ENODEV if sensor is missing

Update the soc-camera i2c code to return -ENODEV if
a camera sensor is missing instead of -ENOMEM.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>