MIPS: MSP: Fix MSP71xx bpci interrupt handler return value

Signed-off-by: Anoop P A <anoop.pa@gmail.com>
To: Ben Hutchings <ben@decadent.org.uk>
To: linux-mips@linux-mips.org
To: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1804/


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