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>

Documentation/devicetree/bindings/net/nfc/st21nfcb.txt

 * STMicroelectronics SAS. ST21NFCB NFC Controller
 
 Required properties:
-- compatible: Should be "st,st21nfcb_i2c".
+- compatible: Should be "st,st21nfcb-i2c".
 - clock-frequency: I²C work frequency.
 - reg: address on the bus
 - interrupt-parent: phandle for the interrupt gpio controller
@@ -20,7 +20,7 @@ Example (for ARM-based BeagleBoard xM with ST21NFCB on I2C2):
 
 	st21nfcb: st21nfcb@8 {
 
-		compatible = "st,st21nfcb_i2c";
+		compatible = "st,st21nfcb-i2c";
 
 		reg = <0x08>;
 		clock-frequency = <400000>;

drivers/nfc/st21nfcb/i2c.c

@@ -373,6 +373,7 @@ static int st21nfcb_nci_i2c_remove(struct i2c_client *client)
 
 #ifdef CONFIG_OF
 static const struct of_device_id of_st21nfcb_i2c_match[] = {
+	{ .compatible = "st,st21nfcb-i2c", },
 	{ .compatible = "st,st21nfcb_i2c", },
 	{}
 };