MIPS: i8259: Correct comment for i8259

The comment for the slave PIC is changed from 8259A-1 to 8259A-2.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
To:  LKML <linux-kernel@vger.kernel.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2693/


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