crypto: arm64/aes-ccm - don't use an atomic walk needlessly

When the AES-CCM code was first added, the NEON register were saved
and restored eagerly, and so the code avoided doing so, and executed
the scatterwalk in atomic context inside the kernel_neon_begin/end
section.

This has been changed in the meantime, so switch to non-atomic
scatterwalks.

Fixes: bd2ad885 ("crypto: arm64/aes-ce-ccm - move kernel mode neon ...")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>