NFC: st21nfcb: Fix logic when running into i2c read retry

When retrying to read the NCI header, the CLF might not be
available the first time. However it may not be successful
the second time and this may cause an error in the function.
Enforce the retrieve data length is as expected.

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