usb: dwc2: Silence warning about supplies during deferred probe

Don't confuse user with meaningless warning about the failure in getting
supplies in case of deferred probe.

Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>