usb: dwc3: omap: improve error handling of dwc3_omap_probe

Improved the error handling of dwc3_omap_probe so that on error
conditions dwc3_omap is left in the original state.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>