soc: qcom: subsys-pil-tz: Reduce serial log spam from the ADSP wdog handler

The watchdog interrupt line from the ADSP, once triggered, is only
de-asserted when the ADSP is shutdown. In the interim, several
interrupts may be received. Don't spam the serial log in the
interrupt handler.

CRs-Fixed: 751552
Change-Id: I39c4a05ab0c15ddf5c95a6b381ea658380eec80d
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>