popen should pclose

```
In function ‘find_readline_so’,
    inlined from ‘main’ at bashreadline.c:163:33:
bashreadline.c:135:17: warning: ‘fclose’ called on pointer returned from a mismatched allocation function [-Wmismatched-dealloc]
  135 |                 fclose(fp);
      |                 ^~~~~~~~~~
bashreadline.c: In function ‘main’:
bashreadline.c:119:14: note: returned from ‘popen’
  119 |         fp = popen("ldd /bin/bash", "r");
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~
```

libbpf-tools/bashreadline.c

@@ -132,7 +132,7 @@ static char *find_readline_so()
 	if (line)
 		free(line);
 	if (fp)
-		fclose(fp);
+		pclose(fp);
 	return result;
 }