power: supply: twl4030-charger: fix OF sibling-node lookup

Use the new of_get_compatible_child() helper to lookup the usb sibling
node instead of using of_find_compatible_node(), which searches the
entire tree from a given start node and thus can return an unrelated
(non-sibling) node.

This also addresses a potential use-after-free (e.g. after probe
deferral) as the tree-wide helper drops a reference to its first
argument (i.e. the parent device node).

While at it, also fix the related phy-node reference leak.

Fixes: f5e4edb8 ("power: twl4030_charger: find associated phy by more reliable means.")
Cc: stable <stable@vger.kernel.org>     # 4.2
Cc: NeilBrown <neilb@suse.de>
Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Sebastian Reichel <sre@kernel.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>