MIPS: ath91: Remove pointless irqdisable/enable

The various interrupt flow handlers in ath79 are cascading interrupt
handlers. They all have 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.

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/10703/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>