nfc: trf7970a: constify several pointers

Several functions do not modify pointed data so arguments and local
variables can be const for correctness and safety.
Signed-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/nfc/trf7970a.c

@@ -643,7 +643,7 @@ static void trf7970a_send_err_upstream(struct trf7970a *trf, int errno)
 }
 
 static int trf7970a_transmit(struct trf7970a *trf, struct sk_buff *skb,
-			     unsigned int len, u8 *prefix,
+			     unsigned int len, const u8 *prefix,
 			     unsigned int prefix_len)
 {
 	struct spi_transfer t[2];
@@ -1387,9 +1387,10 @@ static int trf7970a_is_iso15693_write_or_lock(u8 cmd)
 	}
 }
 
-static int trf7970a_per_cmd_config(struct trf7970a *trf, struct sk_buff *skb)
+static int trf7970a_per_cmd_config(struct trf7970a *trf,
+				   const struct sk_buff *skb)
 {
-	u8 *req = skb->data;
+	const u8 *req = skb->data;
 	u8 special_fcn_reg1, iso_ctrl;
 	int ret;
 
@@ -1791,7 +1792,7 @@ static int _trf7970a_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
 static int trf7970a_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
 			      nfc_digital_cmd_complete_t cb, void *arg)
 {
-	struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
+	const struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
 
 	dev_dbg(trf->dev, "Listen - state: %d, timeout: %d ms\n",
 		trf->state, timeout);
@@ -1803,7 +1804,7 @@ static int trf7970a_tg_listen_md(struct nfc_digital_dev *ddev,
 				 u16 timeout, nfc_digital_cmd_complete_t cb,
 				 void *arg)
 {
-	struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
+	const struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
 	int ret;
 
 	dev_dbg(trf->dev, "Listen MD - state: %d, timeout: %d ms\n",
@@ -1824,7 +1825,7 @@ static int trf7970a_tg_listen_md(struct nfc_digital_dev *ddev,
 
 static int trf7970a_tg_get_rf_tech(struct nfc_digital_dev *ddev, u8 *rf_tech)
 {
-	struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
+	const struct trf7970a *trf = nfc_digital_get_drvdata(ddev);
 
 	dev_dbg(trf->dev, "Get RF Tech - state: %d, rf_tech: %d\n",
 		trf->state, trf->md_rf_tech);
@@ -1974,7 +1975,7 @@ static void trf7970a_shutdown(struct trf7970a *trf)
 	trf7970a_power_down(trf);
 }
 
-static int trf7970a_get_autosuspend_delay(struct device_node *np)
+static int trf7970a_get_autosuspend_delay(const struct device_node *np)
 {
 	int autosuspend_delay, ret;
 
@@ -1987,7 +1988,7 @@ static int trf7970a_get_autosuspend_delay(struct device_node *np)
 
 static int trf7970a_probe(struct spi_device *spi)
 {
-	struct device_node *np = spi->dev.of_node;
+	const struct device_node *np = spi->dev.of_node;
 	struct trf7970a *trf;
 	int uvolts, autosuspend_delay, ret;
 	u32 clk_freq = TRF7970A_13MHZ_CLOCK_FREQUENCY;