iwlwifi: accept EEPROM version 0x423 for iwl6000

A number of these devices have appeared "in the wild", and apparently
the Windows driver is perfectly happy to support this EEPROM version.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Cc: stable@kernel.org
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>