macintosh/windfarm: Remove obsolete cleanup for clientdata

A few new i2c-drivers came into the kernel which clear the clientdata-pointer
on exit or error. This is obsolete meanwhile, the core will do it.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>