MIPS: bpf: Fix branch conditional for BPF_J{GT/GE} cases

MIPS: bpf: Fix branch conditional for BPF_J{GT/GE} cases

The sltiu and sltu instructions will set the scratch register
to 1 if A <= X|K so fix the emitted branch conditional to check
for scratch != zero rather than scratch >= zero which would complicate
the resuling branch logic given that MIPS does not have a BGT or BGET
instructions to compare general purpose registers directly.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: netdev@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7126/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>