bpftool: Cast variable var to long long

When the SIGNED condition is met, the variable `var` should be cast to
`long long` instead of `unsigned long long`.

Signed-off-by: Luo Yifan <luoyifan@cmss.chinamobile.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20241112073701.283362-1-luoyifan@cmss.chinamobile.com

Author: Luo Yifan

tools/bpf/bpftool/btf.c

@@ -289,7 +289,7 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
 			} else {
 				if (btf_kflag(t))
 					printf("\n\t'%s' val=%lldLL", name,
-					       (unsigned long long)val);
+					       (long long)val);
 				else
 					printf("\n\t'%s' val=%lluULL", name,
 					       (unsigned long long)val);