staging: vt6655: add handling memory leak on vnt_start()

There was no code for handling memory leaks of device_init_rings() and
request_irq(). It needs to free allocated memory in the device_init_rings()
, when request_irq() would be failed. Add freeing sequences of irq and
device init rings.

Signed-off-by: Ji-Hun Kim <ji_hun.kim@samsung.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>