iwlagn: fix modinfo display for 135 ucode.

The modinfo report for 135 ucode is iwlwifi-135-IWL135_UCODE_API_MAX.ucode
Change to show the value of the define:  iwlwifi-135-6.ucode

Signed-off-by: Don Fry <donald.h.fry@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>