usb: udc-uclass: Fixed problem when no alias is defined in DT

commit 801f1fa4 "dm: usb: udc: Use SEQ_ALIAS to index the USB gadget
ports" changed the way the udevice if found. It uses the alias to find
a udevice for a given USB port number. In the commit log it was stated
that if no alias is provided, the bind order will be used instead. However
it doesn't work. Fixing this by adding a call to uclass_get_device() if
uclass_get_device_by_seq() fails.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Tested-by: Vignesh R <vigneshr@ti.com>