usb: dwc3: imx8mp: fix error return code in dwc3_imx8mp_probe()

Fix to return a negative error code from the error handling case instead
of 0, as done elsewhere in this function.

Fixes: 6dd25659

 ("usb: dwc3: add imx8mp dwc3 glue layer driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210508015310.1627-1-thunder.leizhen@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>