MIPS: MSP71xx: fix build failures on msp_irq_slp.c

Trying to build MSP4200 VoIP defconfig also fails on msp_irq_slp.c with a
non-existing reference to mask_slp_irq, which is in turn mask_msp_slp_irq.
Passed that, we will also miss a comma when calling
set_irq_chip_and_handler. This patch fixes both issues.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Shane McDonald <mcdonald.shane@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>