ASoC: wcd9330: Avoid codec read/writes if device is down

When SLIMbus is down, read and write codec registers over
SLIMbus cannot be performed. Set codec device down whenever
SLIMbus device down notification is received so that read and
writes can be avoided safely. Later when SLIMbus device up
notification is received, codec device down state will be
cleared and read/writes can be sent as usual.

Change-Id: Ida13003e8123cf2a6b992db6acdff764c32cea51
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>