[media] em28xx: rename em28xx_hint_sensor() to em28xx_detect_sensor()

Now that the board hints and the sensor initialization/configuration have been
separated, em28xx_detect_sensor() is the better name for this function.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>