backlight: lm3630a: Cancel delayed work before destroying workqueue

The interrupt handler queues delayed work to read the interrupt status.
After free_irq() stops the producer, this work can still be waiting on its
timer. destroy_workqueue() cannot drain delayed work that has not yet been
queued by its timer, so the timer can outlive both the workqueue and the
devm-allocated chip containing the work.

Cancel the delayed work synchronously after freeing the IRQ and before
destroying the workqueue. This also waits for any running status read to
finish before the chip's resources are released.

This issue was identified during our ongoing static-analysis research
while reviewing kernel code.

Fixes: 0c2a665a648e ("backlight: add Backlight driver for lm3630 chip")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Co-developed-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Myeonghun Pak <mhun512@gmail.com>
Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://patch.msgid.link/20261003030439.599330-1-mhun512@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>

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