docs: i2c: summary: update I2C specification link

Luckily, the specs are directly downloadable again, so update the link.
Also update its title to the original name "I²C".

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Author: Wolfram Sang

Documentation/i2c/summary.rst

@@ -11,11 +11,9 @@ systems. Some systems use variants that don't meet branding requirements,
 and so are not advertised as being I2C but come under different names,
 e.g. TWI (Two Wire Interface), IIC.
 
-The latest official I2C specification is the `"I2C-bus specification and user
-manual" (UM10204) <https://www.nxp.com/webapp/Download?colCode=UM10204>`_
-published by NXP Semiconductors. However, you need to log-in to the site to
-access the PDF. An older version of the specification (revision 6) is archived
-`here <https://web.archive.org/web/20210813122132/https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_.
+The latest official I2C specification is the `"I²C-bus specification and user
+manual" (UM10204) <https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_
+published by NXP Semiconductors, version 7 as of this writing.
 
 SMBus (System Management Bus) is based on the I2C protocol, and is mostly
 a subset of I2C protocols and signaling. Many I2C devices will work on an