usb: cdns3: core: removed overwriting some error code

Some error code can be preserved, so we can remove overwriting
error code returned by some functions.

Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Reviewed-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>