NFC: st21nfca: Keep st21nfca_gates unchanged in load_session

We need to keep initial st_nci_gates values in order for
nfc_hci_dev_connect_gates to create and open pipe when necessary.

For example after a firmware update CLF pipes are cleared. Changing
pipe values in st21nfca_gates was causing nfc_hci_dev_connect_gates
not using accurate pipes value.

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