crypto: gf128mul - remove incorrect comment

The comment in gf128mul_x8_ble() was copy-and-pasted from gf128mul.h and
makes no sense in the new context.  Remove it.

Cc: Harsh Jain <harsh@chelsio.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>