NFC: st21nfcb: disable irq when st21nfcb is disabled

When st21nfcb is disabled, the irq line may remain active
while no data are available, flooding the system with
irrelevant i2c transaction.

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