MIPS: BPF: Fix stack pointer allocation

Fix stack pointer offset which could potentially corrupt
argument registers in the previous frame. The calculated offset
reflects the size of all the registers we need to preserve so there
is no need for this erroneous subtraction.

[ralf@linux-mips.org: Fixed conflict due to only applying this fix part
of the entire series as part of 4.1 fixes.]

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/10527/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>