arch/mips/net/bpf_jit.c: fix failure check

arch/mips/net/bpf_jit.c: fix failure check

static int pkt_type_offset(void) returned -1 in case of failure, and actual
(positive) offset value in case of success. In the only instance of its usage,
the result was saved to local "unsigned int off" variable, which is used in a
lot of places in the same (large) function, so changing its type could cause
many warnings. So new signed int variable was added.

Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=80371
Reported-by: David Binderman <dcb314@hotmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: kernel-janitors@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: dborkman@redhat.com
Cc: markos.chandras@imgtec.com
Patchwork: https://patchwork.linux-mips.org/patch/7380/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>