IWL6000G2B_UCODE_API_MAX is not defined. ucode_api_max of
IWL_DEVICE_6030 uses IWL6000G2_UCODE_API_MAX. Use this also for
MODULE_FIRMWARE.

Fixes: 9d9b21d1 ("iwlwifi: remove IWL_*_UCODE_API_OK")
Signed-off-by: Jürg Billeter <j@bitron.ch>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>