docs: i2c: rename i2c.svg to i2c_bus.svg

When generating the PDF output, the Documentation/i2c dir
will generate an i2c.pdf. The same happens with i2c.svg:
it will also produce a file with the same name, at the same dir.

This causes errors when building the PDF output. So, rename the
image to i2c_bus.svg.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Link: https://lore.kernel.org/r/ecf3d51909ce46b3e84a1df4b36f07d76989e5da.1586881715.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>