i386 turns out to not have __uint128_t. So confusingly use 64-bit math
instead. Since we're little endian, we can get away with it. Also,
since the counters in quesitons would require billions of iops for
tens of billions of seconds to overflow, and since such data rates are
unlikely for people using i386 for a while, that's OK. The fastest
cards today can't do even a million IOPs.

Noticed by: dim@
Sponsored by: Netflix, Inc