thermal/drivers/qcom/lmh: Fix irq handler return value

After enough invocations the LMh irq is eventually reported as bad, because the
handler doesn't return IRQ_HANDLED, fix this.

Fixes: 53bca371

 ("thermal/drivers/qcom: Add support for LMh driver")
Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20220316180322.88132-1-bjorn.andersson@linaro.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>