bpf: Simplify the calculation of variables

Fix the following coccicheck warnings:

./tools/bpf/bpf_dbg.c:1201:55-57: WARNING !A || A && B is equivalent to
!A || B.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/1614756035-111280-1-git-send-email-jiapeng.chong@linux.alibaba.com