ASoC: da732x: Fix control-less DAPM routes

ASoC: da732x: Fix control-less DAPM routes

Routes without a control must use NULL for the control name. The da732x
driver uses "NULL" instead in a few places. Previous to commit 6ba8000c6150
("ASoC: dapm: Do not pretend to support controls for non mixer/mux widgets")
the DAPM core silently ignored non-NULL controls on non-mixer and non-mux
routes. But starting with that commit it will complain and not add the
route breaking the da732x driver in the process.

This patch replaces the incorrect "NULL" control name with NULL to fix the
issue.

Fixes: 6ba8000c6150 ("ASoC: dapm: Do not pretend to support controls for non mixer/mux widgets")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org