cpuidle/powerpc: Fix target residency initialisation in pseries cpuidle

Remove the redundant target residency initialisation in pseries_cpuidle_driver_init().
This is currently over-writing the residency time updated as part of the static
table, resulting in  all the idle states having the same target
residency of 100us which is incorrect. This may result in the menu governor making
wrong state decisions.

Signed-off-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>