MIPS: MSP71xx: remove unused plat_irq_dispatch() argument

Remove unused argument to make the plat_irq_dispatch() function
declaration similar to the realization of other platforms.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Cc: Linux MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7538/


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