Input: cyttsp4 - kfree xfer_buf on error path in probe()

If probe() fails after cd->xfer_buf allocated, it will not freed.
Added kfree(cd->xfer_buf) with and error label.

Signed-off-by: Ferruh Yigit <fery@cypress.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>