tools/bpf: Fix the wrong format specifier

The format specifier of "unsigned int" in printf() should be "%u", not
"%d".

Signed-off-by: Zhu Jun <zhujun2@cmss.chinamobile.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20240724111120.11625-1-zhujun2@cmss.chinamobile.com