NFC: st21nfcb: Fix scripts/checkpatch.pl error "code indent should use tabs where possible"

Fixing scripts/checkpatch.pl error "code indent should use tabs where possible" in:
- i2c.c in st21nfcb_nci_irq_thread_fn function.
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>