power: twl4030_charger: find associated phy by more reliable means.

twl4030_charger currently finds the associated phy
using usb_get_phy() which will return the first USB2 phy.
If your platform has multiple such phys (as mine does),
this is not reliable (and reliably fails on the GTA04).

Change to use devm_usb_get_phy_by_node(), having found the
node by looking for an appropriately named sibling in
device-tree.

This makes usb-charging dependent on correct device-tree
configuration.

Acked-By: Sebastian Reichel <sre@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>