NFC: pn533: use constant off-stack buffer for sending acks

fix for WARN:

usb 3-2.4.1: NFC: Exchanging data failed (error 0x13)
llcp: nfc_llcp_recv: err -5
llcp: nfc_llcp_symm_timer: SYMM timeout
------------[ cut here ]------------
WARNING: CPU: 1 PID: 26397 at .../drivers/usb/core/hcd.c:1584 usb_hcd_map_urb_for_dma+0x370/0x550
transfer buffer not dma capable
[...]
Workqueue: events nfc_llcp_timeout_work [nfc]
Call Trace:
 ? dump_stack+0x46/0x5a
 ? __warn+0xb9/0xe0
 ? warn_slowpath_fmt+0x5a/0x80
 ? usb_hcd_map_urb_for_dma+0x370/0x550
 ? usb_hcd_submit_urb+0x2fb/0xa60
 ? dequeue_entity+0x3f2/0xc30
 ? pn533_usb_send_ack+0x5d/0x80 [pn533_usb]
 ? pn533_usb_abort_cmd+0x13/0x20 [pn533_usb]
 ? pn533_dep_link_down+0x32/0x70 [pn533]
 ? nfc_dep_link_down+0x87/0xd0 [nfc]
[...]
usb 3-2.4.1: NFC: Exchanging data failed (error 0x13)
llcp: nfc_llcp_recv: err -5
llcp: nfc_llcp_symm_timer: SYMM timeout
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/pn533/i2c.c

@@ -51,7 +51,7 @@ static int pn533_i2c_send_ack(struct pn533 *dev, gfp_t flags)
 {
 	struct pn533_i2c_phy *phy = dev->phy;
 	struct i2c_client *client = phy->i2c_dev;
-	u8 ack[6] = {0x00, 0x00, 0xff, 0x00, 0xff, 0x00};
+	static const u8 ack[6] = {0x00, 0x00, 0xff, 0x00, 0xff, 0x00};
 	/* spec 6.2.1.3:  Preamble, SoPC (2), ACK Code (2), Postamble */
 	int rc;
 

drivers/nfc/pn533/usb.c

@@ -148,11 +148,11 @@ static int pn533_submit_urb_for_ack(struct pn533_usb_phy *phy, gfp_t flags)
 static int pn533_usb_send_ack(struct pn533 *dev, gfp_t flags)
 {
 	struct pn533_usb_phy *phy = dev->phy;
-	u8 ack[6] = {0x00, 0x00, 0xff, 0x00, 0xff, 0x00};
+	static const u8 ack[6] = {0x00, 0x00, 0xff, 0x00, 0xff, 0x00};
 	/* spec 7.1.1.3:  Preamble, SoPC (2), ACK Code (2), Postamble */
 	int rc;
 
-	phy->out_urb->transfer_buffer = ack;
+	phy->out_urb->transfer_buffer = (u8 *)ack;
 	phy->out_urb->transfer_buffer_length = sizeof(ack);
 	rc = usb_submit_urb(phy->out_urb, flags);