cpufreq: qcom-hw: Disable LMH irq when disabling policy

If LMH (Limits Management Hardware) is available, when a policy is
disabled by unplugging the last online CPU of policy->cpus, the LMH
irq is left enabled.
When the policy is re-enabled with any of the CPU in policy->cpus
being plugged in, qcom_cpufreq_ready() re-enables the irq. This
triggers the following warning:
[  379.160106] Unbalanced enable for IRQ 154
[  379.160120] WARNING: CPU: 7 PID: 48 at kernel/irq/manage.c:774 __enable_irq+0x84/0xc0
Thus disable the irq.

This patch also makes the check against throttle_irq consistent,
0 being theoretically valid.

Fixes: a1eb080a ("cpufreq: qcom-hw: provide online/offline operations")
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>