serial: vt8500: fix possible memory leak in vt8500_serial_probe()
vt8500_port is malloced in vt8500_serial_probe() and should be freed
before leaving from the error handling cases, otherwise it will
cause memory leak.
Fix it by move the allocation of vt8500_port after those test.
dpatch engine is used to auto generate this patch.
(https://github.com/weiyj/dpatch)