nfc: st-nci: Remove data from ack_pending_q when receiving a SYNC_ACK

When receiving a NDLC PCB_SYNC_ACK the pending data was never
removed from ack_pending_q and cleared.

Cc: stable@vger.kernel.org
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>