cfg80211: use BIT_ULL in cfg80211_parse_mbssid_data()

The seen_indices variable is u64 and in other parts of the code we
assume mbssid_index_ie[2] can be up to 45, so we should use the 64-bit
versions of BIT, namely, BIT_ULL().

Reported-by: Dan Carpented <dan.carpenter@oracle.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>