media: v4l2-common: v4l2_spi_subdev_init : generate unique name

While v4l2_i2c_subdev_init does give a unique name to the subdev, matching
the one appearing in dmesg for messages generated by dev_info and friends
(e.g. imx185 30-0010), v4l2_spi_subdev_init does a poor job, copying only
the driver name, but not the dev_name(), yielding e.g. "imx185", but
missing the "spi1.1" part, and not generating a unique name.

Fix that.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>