bpf: Fix a spelling typo in bpf_atomic_alu_string disasm

The name string for BPF_XOR is "xor", not "or". Fix it.

Fixes: 981f94c3 ("bpf: Add bitwise atomic instructions")
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Brendan Jackman <jackmanb@google.com>
Link: https://lore.kernel.org/bpf/20210325134141.8533-1-xukuohai@huawei.com