[PATCH v2] Docs: Fixes link to I2C specification

[Deep Majumder <deep@fastmail.in>]

The link to the I2C specification is broken and is replaced in this
patch by one that points to Rev 6 (2014) of the specification.
Although `https://www.nxp.com" hosts the Rev 7 (2021) of this
specification, it is behind a login-wall and thus cannot be used.
Thus, an additional link has been added (which doesn't require a login)
and the NXP official docs link has been updated. The additional link is
not the Wayback Machine link since it seems that the PDF has not been
archived.

Signed-off-by: Deep Majumder <deep@fastmail.in>
---
 Documentation/i2c/summary.rst | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst
index 136c4e333be7..3395e2e46d9c 100644
--- a/Documentation/i2c/summary.rst
+++ b/Documentation/i2c/summary.rst
@@ -11,9 +11,11 @@ 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 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.
+The official I2C specification (revision 7) is the `"I2C-bus specification and user
+manual" (UM10204) <https://www.nxp.com/webapp/Download?colCode=UM10204&location=null>`_
+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 available
+`here <https://www.pololu.com/file/0J435/UM10204.pdf>`_.
 
 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
-- 
2.30.2