mhi: core: handle vote APIs cleanly during power on/off transitions

When a client votes at a time of powering on or off the device,
it is possible the counts can go mismatched and host may assert.
Avoid these issues by clearing the votes at power on and do not
assert if client unvotes when device is inactive.

Change-Id: Iee7b51f11b6beaa11e7f0f5fcde416f8537f355c
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>