This patch simplifies the LRW template to recompute the LRW tweaks from
scratch in the second pass and thus also removes the need to allocate a
dynamic buffer using kmalloc().
As discussed at [1], the use of kmalloc causes deadlocks with dm-crypt.
PERFORMANCE MEASUREMENTS (x86_64)
Performed using: https://gitlab.com/omos/linux-crypto-bench
Crypto driver used: lrw(ecb-aes-aesni)
The results show that the new code has about the same performance as the
old code. For 512-byte message it seems to be even slightly faster, but
that might be just noise.