mfd: twl6040: Remove obsolete cleanup for i2c 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 This is obsolete meanwhile, the core will do it.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: Samuel Ortiz <sameo@linux.intel.com>