usb: dwc3: fix the error returned with usb3_phy failure

When there is an error with the usb3_phy probe or absence, the error returned
is erroneously for usb2_phy.

Cc: <stable@vger.kernel.org>
Signed-off-by: Ruchika Kharwar <ruchika@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>