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 <[e-mail]>
Acked-by: Wolfram Sang <[e-mail]>
Link: https://lore.kernel.org/r/ecf3d5[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/i2c/i2c.svg Documentation/i2c/i2c_bus.svg

···
    xmlns="http://www.w3.org/2000/svg"
    xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
    xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
-   sodipodi:docname="i2c.svg"
+   sodipodi:docname="i2c_bus.svg"
    inkscape:version="0.92.3 (2405546, 2018-03-11)"
    version="1.1"
    id="svg2"

Documentation/i2c/summary.rst

···
 Using the terminology from the official documentation, the I2C bus connects
 one or more *master* chips and one or more *slave* chips.
 
-.. kernel-figure::  i2c.svg
+.. kernel-figure::  i2c_bus.svg
    :alt:    Simple I2C bus with one master and 3 slaves
 
    Simple I2C bus