usb: dwc3: gadget: use explicit 0 for success in __dwc3_gadget_kick_transfer()

usb: dwc3: gadget: use explicit 0 for success in __dwc3_gadget_kick_transfer()

Smatch warns that __dwc3_gadget_kick_transfer() might be missing an
error code when returning 'ret' at line 1691.

While 'ret' is guaranteed to be 0 at this point, returning an explicit 0
improves readability by removing a level of indirection and clarifies
the intent that this is a successful "no-op" path. This change also
silences the Smatch warning.

Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Zeeshan Ahmad <zeeshanahmad022019@gmail.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://patch.msgid.link/20260306090643.47383-1-zeeshanahmad022019@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>