NFC: dts: st21nfcb: Fix compatible string spelling to follow other drivers

Other drivers are following the following compatible string format for dts:
s/_/-/

Because some devices may still use the previous string, the new corrected
string is added to the of_device_id table.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/nfc/st21nfcb/i2c.c b/drivers/nfc/st21nfcb/i2c.c
index 01ba865..b65847c 100644
--- a/drivers/nfc/st21nfcb/i2c.c
+++ b/drivers/nfc/st21nfcb/i2c.c
@@ -373,6 +373,7 @@
 
 #ifdef CONFIG_OF
 static const struct of_device_id of_st21nfcb_i2c_match[] = {
+	{ .compatible = "st,st21nfcb-i2c", },
 	{ .compatible = "st,st21nfcb_i2c", },
 	{}
 };