Do not write to EEPROM when turning screen on/off.

The card emulation duration is kept in EEPROM, and does not need to
be re-configured. Just turning the polling loop off is enough.

Change-Id: I25ee443d04635b3434dabf675ad5a32c4f0f468c

jni/com_android_nfc_NativeNfcManager.cpp

@@ -1510,7 +1510,7 @@ static void nfc_jni_stop_discovery_locked(struct nfc_jni_native_data *nat)
    }
 
    discovery_cfg.PollDevInfo.PollEnabled = 0;
-   discovery_cfg.Duration = 0xffffffff;
+   discovery_cfg.Duration = 300000; /* in ms */
    /*discovery_cfg.NfcIP_Mode = phNfc_eInvalidP2PMode;*/
    discovery_cfg.NfcIP_Mode = phNfc_eDefaultP2PMode;
    discovery_cfg.NfcIP_Tgt_Disable = TRUE;