arch: removed unnecessary call in `seccomp_add_arch`.
arch: removed unnecessary call in `seccomp_add_arch`.

Some logic in the implementation of `seccomp_add_arch` can never
be reached and `arch_def_lookup` was called redundantly.

Signed-off-by: Jiannan Guo <91d7eeb83d08be0dc56ea674009c4b53383e15b3@gmail.com>
[PM: update subject line]
Signed-off-by: Paul Moore <a027184a55211cd23e3f3094f1fdc728df5e0500@paul-moore.com>

seccomp/libseccomp,seccomp/libseccomp,seccomp/libseccomp