crypto: sun4i-ss - simplify the appended bit assignment

A bit is appended at the end of the input buffer for sha1. Simplify the
code assigning it.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>