bpf, libbpf: Fix ___bpf_kretprobe_args1(x) macro definition

Use PT_REGS_RC instead of PT_REGS_RET to get ret correctly.

Fixes: df8ff35 ("libbpf: Merge selftests' bpf_trace_helpers.h into libbpf's bpf_tracing.h")
Signed-off-by: Wenbo Zhang <ethercflow@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200315083252.22274-1-ethercflow@gmail.com

tools/lib/bpf/bpf_tracing.h

@@ -390,7 +390,7 @@ ____##name(struct pt_regs *ctx, ##args)
 
 #define ___bpf_kretprobe_args0() ctx
 #define ___bpf_kretprobe_args1(x) \
-	___bpf_kretprobe_args0(), (void *)PT_REGS_RET(ctx)
+	___bpf_kretprobe_args0(), (void *)PT_REGS_RC(ctx)
 #define ___bpf_kretprobe_args(args...) \
 	___bpf_apply(___bpf_kretprobe_args, ___bpf_narg(args))(args)