iwlwifi: remove upper case letters in sku_capa_band_*_enable

The sku_capa_band_24GHz_enable and sku_capa_band_52GHz_enable symbols
cause checkpatch to complain whenever we use them.  To prevent this,
convert them to all lower case.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>