usb: dwc3: Remove redundant test

usb: dwc3: Remove redundant test

In dwc3_ep0_complete_data there is a test for 'r' being null and the
code will return at that point if so. After that point 'r' is guaranteed
to not be null and testing for that is redundant. Remove the test for
'r' being non-null.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Reviewed-by: Marek Vasut <marek.vasut@mailbox.org>
Link: https://lore.kernel.org/r/20250929-dwc3_ep0-v1-1-1d5c58933bde@linaro.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>