USB: chipidea: msm: fix ulpi-node lookup

Fix child-node lookup during probe, which ended up searching the whole
device tree depth-first starting at the parent rather than just matching
on its children.

Note that the original premature free of the parent node has already
been fixed separately, but that fix was apparently never backported to
stable.

Fixes: 47654a16 ("usb: chipidea: msm: Restore wrapper settings after reset")
Fixes: b74c4315 ("usb: chipidea: msm: ci_hdrc_msm_probe() missing of_node_get()")
Cc: stable <stable@vger.kernel.org>     # 4.10: b74c4315
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>