MIPS: MSP71xx: Fix build error

When CONFIG_MIPS_MT_SMP is enabled, the following compilation error
occurs:

arch/mips/pmcs-msp71xx/msp_irq_cic.c:134: error: ‘irq’ undeclared

This code clearly never saw a compiler.
The surrounding code suggests, that 'd->irq' was intended, not
'irq'.

This error was found with vampyr.

Signed-off-by: Stefan Hengelein <stefan.hengelein@fau.de>
Fixes: d7881fbd

 ("MIPS: msp71xx: Convert to new irq_chip functions")
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8116/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>