crypto: sha1_generic - add cra_priority

sha1-generic had a cra_priority of 0, so it wasn't possible to have a
lower priority SHA-1 implementation, as is desired for sha1_mb which is
only useful under certain workloads and is otherwise extremely slow.
Change it to priority 100, which is the priority used for many of the
other generic algorithms.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>