iwlwifi: return ucode errors from station management

When station management calls to ucode return
an error we could previously do nothing, but
now that almost all calls are synchronous we
can actually let the error bubble up. Use EIO
as the error as it best indicates a problem
with the device.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>