msm: camera: isp: Move event payload to free list in deinit

As a safety check, to prevent any payload leaks from unclean stop,
move all the payloads back to free list on Deinit HW which happens
when the HW is being completely shut and no more processing is required.
Also, in runtime, if ever we run out of payloads, its a fatal error,
since the IRQ will be dropped. Given that there are 256 payloads, unless
there is an IRQ storm causing system freeze or some other deadlock
preventing bottom half to run and return the payload, such an error
should not happen. So changing the error to BUG().

Change-Id: Iffaea4a9fc9aceebcf431aa27d5421aca82d7cc0
Signed-off-by: Harsh Shah <harshs@codeaurora.org>