test_bpf: Rename second ALU64_SMOD_X to ALU64_SMOD_K

Currently, there are two test cases with same name
"ALU64_SMOD_X: -7 % 2 = -1", the first one is right,
the second one should be ALU64_SMOD_K because its
code is BPF_ALU64 | BPF_MOD | BPF_K.

Before:
test_bpf: #170 ALU64_SMOD_X: -7 % 2 = -1 jited:1 4 PASS
test_bpf: #171 ALU64_SMOD_X: -7 % 2 = -1 jited:1 4 PASS

After:
test_bpf: #170 ALU64_SMOD_X: -7 % 2 = -1 jited:1 4 PASS
test_bpf: #171 ALU64_SMOD_K: -7 % 2 = -1 jited:1 4 PASS

Fixes: daabb2b0 ("bpf/tests: add tests for cpuv4 instructions")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231207040851.19730-1-yangtiezhu@loongson.cn


Signed-off-by: Alexei Starovoitov <ast@kernel.org>