iwlwifi: pcie: reset write pointer on ict reset

Since the CSR_DRAM_INIT_TBL_WRITE_POINTER bit wasn't set
on ict reset, in some flows (like disable ict followed by
immediate reset ict) the driver and hardware went out
of sync (the driver cleared the ict_index, while the hw
kept it intact).

Fix it by setting the flag when resetting ict.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>