usb: musb: mpfs: Fix error codes in probe()

These error paths return success but they need to return a negative
error code.

Fixes: 7a96b6ea

 ("usb: musb: Add support for PolarFire SoC's musb controller")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YrVmLEc/FOEzNdzj@kili
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>