iwlwifi: Fix firmware name maximum length definition

Previous patch had changed firmware name convention for
new generation product. The firmware name is now longer
than the former convention. Adapt max firmware name length
to the new convention.

Fixes: e1ba684f ("iwlwifi: 8000: fix MODULE_FIRMWARE input")
Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>