usb: dwc3: Handle case where setup_phy is not needed

If CONFIG_PHY is not enabled then the dwc3_setup_phy()
returns ENOTSUPP which can be still valid and intentional
so modify error check to handle this -ENOTSUPP.

The same error handling exists in drivers/usb/host/xhci-dwc3.c already
added by commit d648a50c ("dwc3: move phy operation to core.c").

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>