i2c: Let checkpatch shout on users of the legacy model

As suggested by Mauro Carvalho Chehab.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>

Documentation/feature-removal-schedule.txt

@@ -340,7 +340,8 @@ Who:  Krzysztof Piotr Oledzki <ole@ans.pl>
 ---------------------------
 
 What:	i2c_attach_client(), i2c_detach_client(), i2c_driver->detach_client()
-When:	2.6.29 (ideally) or 2.6.30 (more likely)
+When:	2.6.30
+Check:	i2c_attach_client i2c_detach_client
 Why:	Deprecated by the new (standard) device driver binding model. Use
 	i2c_driver->probe() and ->remove() instead.
 Who:	Jean Delvare <khali@linux-fr.org>