add i2c_device_address member to nfc_pn544_device_t

Add I2C slave address. Multiple I2C addresses are possible
for PN544 module. Configure address according to board design.

Change-Id: I847e8f3db631f5039cf15143a9982f4b9b209f27
diff --git a/modules/nfc/nfc_hw_example.c b/modules/nfc/nfc_hw_example.c
index 9769282..54c9c56 100644
--- a/modules/nfc/nfc_hw_example.c
+++ b/modules/nfc/nfc_hw_example.c
@@ -44,6 +44,7 @@
         dev->linktype = PN544_LINK_TYPE_INVALID;
         dev->device_node = NULL;
         dev->enable_i2c_workaround = 0;
+        dev->i2c_device_address = 0;
 
         *device = (hw_device_t*) dev;
         return 0;