ASoC: wcd-spi: fix clock disable request during shutdown

It is possible that there could be pending delayed request to disable
the clock while the manager driver has already raised shutdown event.
In such cases, the delayed clock disable request will be made after
shutdown, resulting in unclocked access on the SPI bus. Fix this by
intercepting the shutdown event to flush the clock votes and disable
the clock.

CRs-Fixed: 1091032
Change-Id: I53a3a9aa540c10932eed7fa29ce7c6050504a9a0
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>