drivers: mfd: Fix sido-buck voltage output on wcd9335

vdd-cx supply is derived from sido-buck and is connected
to wcd9335 codec. vdd-cx supply is suddenly dropping to zero
during playback usecase that is causing no response from
codec for slimbus read/writes. Add changes to avoid sudden
drop of vdd-cx supply to wcd9335 codec.

Change-Id: I72c85bc46c41771eb969de452cf3f241ed6577f2
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>