media: i2c: vgxy61: Fix device name

Rename 'st-vgxy61' to 'vgxy61', dropping the vendor prefix to follow the
same naming scheme as the vast majority of device drivers.
The device tree binding does not fall into binding rename exceptions and
therefore must not be changed. Keep its legacy name.

Signed-off-by: Benjamin Mugnier <benjamin.mugnier@foss.st.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>