usb: dwc2: pci: Fix error return code in dwc2_pci_probe()

Fix to return error code -ENOMEM from the alloc fail error handling
case instead of 0, as done elsewhere in this function.

Fixes: ecd29dab ("usb: dwc2: pci: Handle error cleanup in probe")
Reviewed-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>