crypto: aesni - add compatibility with IAS

Clang's integrated assembler complains "invalid reassignment of
non-absolute variable 'var_ddq_add'" while assembling
arch/x86/crypto/aes_ctrby8_avx-x86_64.S. It was because var_ddq_add was
reassigned with non-absolute values several times, which IAS did not
support. We can avoid the reassignment by replacing the uses of
var_ddq_add with its definitions accordingly to have compatilibility
with IAS.

Link: https://github.com/ClangBuiltLinux/linux/issues/1008


Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Reported-by: Fangrui Song <maskray@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # build+boot Linux v5.7.5; clang v11.0.0-git
Signed-off-by: Jian Cai <caij2003@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>