clocksource/drivers/mips-gic-timer: Remove pointless irq_save,restore

The function gic_next_event is always called with interrupts disabled, so
the local_irq_save / local_irq_restore are pointless - remove them.

[Daniel Lezcano: Fixed warning by removing unused variable 'flags']

Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Suggested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>