usbg: Return USBG_ERROR_PATH_TOO_LONG error when it happens

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>
Acked-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>