MIPS: alchemy: Remove pointless irqdisable/enable

bcsr_csc_handler() is a cascading interrupt handler. It has a
disable_irq_nosync()/enable_irq() pair around the generic_handle_irq()
call. The value of this disable/enable is zero because its a complete
noop:

disable_irq_nosync() merily increments the disable count without
actually masking the interrupt. enable_irq() soleley decrements the
disable count without touching the interrupt chip. The interrupt
cannot arrive again because the complete call chain runs with
interrupts disabled.

Remove it.

[ralf@linux-mips.org: Fold in followup fix from Thomas Gleixner.]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Patchwork: https://patchwork.linux-mips.org/patch/10702/
Patchwork: https://patchwork.linux-mips.org/patch/10708/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/alchemy/devboards/bcsr.c

@@ -8,6 +8,7 @@
  */
 
 #include <linux/interrupt.h>
+#include <linux/irqchip/chained_irq.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
 #include <linux/irq.h>
@@ -88,10 +89,11 @@ EXPORT_SYMBOL_GPL(bcsr_mod);
 static void bcsr_csc_handler(unsigned int irq, struct irq_desc *d)
 {
 	unsigned short bisr = __raw_readw(bcsr_virt + BCSR_REG_INTSTAT);
+	struct irq_chip *chip = irq_desc_get_chip(d);
 
-	disable_irq_nosync(irq);
+	chained_irq_enter(chip, d);
 	generic_handle_irq(bcsr_csc_base + __ffs(bisr));
-	enable_irq(irq);
+	chained_irq_exit(chip, d);
 }
 
 static void bcsr_irq_mask(struct irq_data *d)