usb: dwc3: gadget: Don't prepare TRBs if no space

If trbs_left == 0, we don't have any space left in the TRB ring so don't
prepare anything.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
1 file changed