bpf: fix 32-bit divide by zero

due to some JITs doing if (src_reg == 0) check in 64-bit mode
for div/mod operations mask upper 32-bits of src register
before doing the check

Fixes: 62258278 ("net: filter: x86: internal BPF JIT")
Fixes: 7a12b503

 ("sparc64: Add eBPF JIT.")
Reported-by:  <syzbot+48340bb518e88849e2e3@syzkaller.appspotmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>