NFC: st21nfca: Fix st21nfca_hci_remove_len_crc tail room handling

There is no byte stuffing when data are stored in skb.
TAILROOM is 2 byte crc + 1 byte eof.

st21nfca_hci_remove_len_crc was doing an incorrect operation on
the TAILROOM data.
If shdlc timer T2 is triggered, it will request to send the same data.
Before every hci data was lost after st21nfca_hci_remove_len_crc.

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