powerpc/mpc5200: Make internal 5200 PIC the default interrupt controller

The MPC5200 internal interrupt controller setup function needs to set
the default interrupt controller when it is called. Without this
irq_create_of_mapping() cannot be called without first determining
the pointer to the irq controller (ie. call with controller = NULL).

Reported-by: Steven Cavanagh <[e-mail]>
Signed-off-by: Grant Likely <[e-mail]>

arch/powerpc/platforms/52xx/mpc52xx_pic.c

···
 	if (!mpc52xx_irqhost)
 		panic(__FILE__ ": Cannot allocate the IRQ host\n");
 
+	irq_set_default_host(mpc52xx_irqhost);
+
 	pr_info("MPC52xx PIC is up and running!\n");
 }