ASoC: mt8173-rt5650: fix child-node lookup

This driver used the wrong OF-helper when looking up the optional
capture-codec child node during probe. Instead of searching just
children of the sound node, a tree-wide depth-first search starting at
the unrelated platform node was done. Not only could this end up
matching an unrelated node or no node at all; the platform node could
also be prematurely freed since of_find_node_by_name() drops a reference
to its first argument. This particular pattern has been observed leading
to crashes after probe deferrals in other drivers.

Fix this by dropping the broken call to of_find_node_by_name() and
keeping only the second, correct lookup using of_get_child_by_name()
while taking care not to bail out if the optional node is missing.

Note that this also addresses two capture-codec node-reference leaks
(one for each of the original helper calls).

Compile tested only.

Fixes: d349caeb0510 ("ASoC: mediatek: Add second I2S on mt8173-rt5650 machine driver")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>