usb: dwc2: Return errors from PHY

When searching for PHYs, any error was treated as if the PHY did not
exist or was not specified. Thus the probe function did not
correctly return error conditions such as -EPROBE_DEFER.

Fixed so that only a non-existing PHY is ignored and any other error
is returned.

Acked-by: Eric Anholt <eric@anholt.net>
Reported-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>