crypto: stm32 - Remove unused hdev->err field

The variable hdev->err is never read so it can be removed.

Also remove a spurious inclusion of linux/crypto.h.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>