Input: synaptics-rmi4 - use of_get_child_by_name() to fix refcount

Calling of_find_node_by_name() assumes that the caller has incremented
the refcount of the of_node being passed in. Currently, the caller is
not incrementing the refcount of the of_node which results in the node
being prematurely freed when of_find_node_by_name() calls of_node_put()
on it. Instead use of_get_child_by_name() which does not call put on the
of_node.

Signed-off-by: Andrew Duggan <aduggan@synaptics.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>