MIPS: Malta SMTC: Fix build.

Commit a561b02a2577aec51277ba39c82bd192a79c0267 (lmo) rsp.
7c8d948f (kernel.org) ["MIPS: i8259: Convert
to new irq_chip functions"] missed one location to modify resulting in
build breakage.

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