tweak belt-dwp bundled ghash, use polyval as inner

[makavity]

 name                   before.txt ns/iter  after.txt ns/iter   diff ns/iter   diff %  speedup 
 decrypt_aad_only_16kb  18,386 (891 MB/s)   1,523 (10757 MB/s)       -16,863  -91.72%  x 12.07 
 decrypt_msg_only_16kb  91,471 (179 MB/s)   73,526 (222 MB/s)        -17,945  -19.62%   x 1.24 
 encrypt_aad_only_16kb  18,268 (896 MB/s)   1,492 (10981 MB/s)       -16,776  -91.83%  x 12.24 
 encrypt_msg_only_16kb  90,306 (181 MB/s)   73,763 (222 MB/s)        -16,543  -18.32%   x 1.22 

I think, closes RustCrypto/universal-hashes#236