usb: phy: add static inline wrapper for devm_usb_get_phy_by_node

The newly introduced devm_usb_get_phy_by_node function only has
an extern declaration, but no alternative for the case that
CONFIG_USB_PHY is disabled, which leads to a build error when
it is used anyway:

drivers/power/twl4030_charger.c: In function 'twl4030_bci_probe':
drivers/power/twl4030_charger.c:648:23: error: implicit declaration of function 'devm_usb_get_phy_by_node' [-Werror=implicit-function-declaration]
    bci->transceiver = devm_usb_get_phy_by_node(

This adds the wrapper in the same way that we have one for
all other usb-phy API functions.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: e842b84c ("usb: phy: Add interface to get phy give of device_node.")
Signed-off-by: Felipe Balbi <balbi@ti.com>