crypto: x86/sha - Eliminate casts on asm implementations

In order to avoid CFI function prototype mismatches, this removes the
casts on assembly implementations of sha1/256/512 accelerators. The
safety checks from BUILD_BUG_ON() remain.

Additionally, this renames various arguments for clarity, as suggested
by Eric Biggers.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>