crypto: lib - add module license to libsha1

libsha1 can be a module, so it needs a MODULE_LICENSE.

Fixes: ec8f7f48 ("crypto: lib - make the sha1 library optional")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>