FROMGIT: crypto: chacha20-generic - don't unnecessarily use atomic walk

chacha20-generic doesn't use SIMD instructions or otherwise disable
preemption, so passing atomic=true to skcipher_walk_virt() is
unnecessary.

Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

(cherry picked from commit 5e04542a0e0763294e9fced73a149c38c4e0cee5
 https://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git

 master)
Bug: 112008522
Test: As series, see Ic61c13b53facfd2173065be715a7ee5f3af8760b
Change-Id: I28a63d6f8aa59f60aed8d35107b3c546ca5152f7
Signed-off-by: Eric Biggers <ebiggers@google.com>