NFC: st-nci: Fix incorrect spi buffer size

When sending data over SPI, the maximum expected length is the maximum
nci packet payload + data header size + the frame head room (1 for the
ndlc header) + the frame trail room (0).

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