Add missing fallthrough to fbcode/faiss/utils/hamming_distance/neon-inl.h

Differential Revision: D52436745

fbshipit-source-id: 7e4c55a8255b2f25b3394146a24d1af698b3b2e9

Author: r-barnes

faiss/utils/hamming_distance/neon-inl.h

@@ -338,6 +338,7 @@ struct HammingComputerDefault {
                     len -= 8;
                     accu += popcount64(a64[i] ^ b64[i]);
                     i++;
+                    [[fallthrough]];
                     case 7:
                         accu += popcount64(a64[i] ^ b64[i]);
                         i++;