ASoC: wm9713: Use empty struct initializer

{ 0 } only clears the first member of the structure.

The first member of the snd_soc_dapm_update struct is a pointer,
and writing 0 to a pointer results in a sparse warning.

Use the empty struct initializer that clears all the struct members
and fixes the sparse warning.

Cc: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>