genirq/timings: Fix error return code in irq_timings_test_irqs()

Return a negative error code from the error handling case instead of 0, as
done elsewhere in this function.

Fixes: f52da98d ("genirq/timings: Add selftest for irqs circular buffer")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210811093333.2376-1-thunder.leizhen@huawei.com