MIPS: R2: Fix local_irq_save()

local_irq_restore uses di which saves the whole status content, not
just the IE bit resulting in  local_irq_restore() to fail.  This only
happens if both CONFIG_CPU_MIPSR2 and CONFIG_IRQ_CPU are enabled.

Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>