MIPS: SMTC: fix implicit declaration of set_vi_handler

MIPS: SMTC: fix implicit declaration of set_vi_handler

This patch fixes the following implicit declaration while building with
MIPS SMTC support enabled:

arch/mips/kernel/smtc.c: In function 'setup_cross_vpe_interrupts':
arch/mips/kernel/smtc.c:1205:2: error: implicit declaration of function
'set_vi_handler' [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4931/
Signed-off-by: John Crispin <blogic@openwrt.org>