ltq-deu: convert SHA1 after library impl of SHA1 was removed

The <linux/cryptohash.h> was removed with Linux 5.8, because it only
contained the library implementation of SHA1, which was folded
into <crypto/sha.h>.
So switch this driver away from using <linux/cryptohash.h>.

Signed-off-by: Daniel Kestrel <kestrel1974@t-online.de>