iwlwifi: add new pci id for 6x35 series

some new thinkpad laptops use intel chip with new pci id need be added
lspci -vnn output:
 Network controller [0280]: Intel Corporation Centrino Advanced-N 6235
 [8086:088f] (rev 24)
 Subsystem: Intel Corporation Device [8086:5260]

Signed-off-by: Shuduo Sang <sangshuduo@gmail.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>