The previous change to allow hashing from states other than the
initial broke compilation on i386 because the inline assembly
tried to squeeze a u64 into a 32-bit register.  As we've already
checked for 32-bit overflows we can simply truncate it to u32,
or unsigned long so that we don't truncate at all on x86-64.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>