crypto: stm32/hash - Simplify code

We are passing (rctx->flags & HASH_FLAGS_FINUP) as indicator
for the final request but we already know this to be true since
we are in the (final) arm of an if-statement set from the same
flag. Just open-code it as true.

Acked-by: Lionel Debieve <lionel.debieve@foss.st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>