mfd: wcd9xxx: Clear sva engine interrupt before dispatch

It is possible that the SVASS_ENGINE interrupt from codec can be
triggered when previous interrupt is still under processing in threaded
context. In order to not lose interrupts in such a case, clear the
SVASS_ENGINE codec interrupt before it is dispatched to the threaded
interrupt handler.

Change-Id: I19e41cf14cf854e926def869c6a386e595d1451e
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>