iwlwifi: fix 11n_disable EEPROM refactoring regression

My commit 26a7ca9a ("iwlwifi: refactor EEPROM reading/parsing")
broke the 11n_disable module parameter's BIT(0) to disable all HT
operation (using the other bits to disable aggregation only was
unaffected). Restore this by overriding the SKU when parsing the
EEPROM if the module parameter is set.

Reported-by: Matthijs Kooijman <matthijs@stdin.nl>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>