NFC: nxp-nci: Fix NULL pointer dereference after I2C communication error

I2C communication errors (-EREMOTEIO) during the IRQ handler of nxp-nci
result in a NULL pointer dereference at the moment:

    BUG: kernel NULL pointer dereference, address: 0000000000000000
    Oops: 0002 [#1] PREEMPT SMP NOPTI
    CPU: 1 PID: 355 Comm: irq/137-nxp-nci Not tainted 5.4.0-rc6 #1
    RIP: 0010:skb_queue_tail+0x25/0x50
    Call Trace:
     nci_recv_frame+0x36/0x90 [nci]
     nxp_nci_i2c_irq_thread_fn+0xd1/0x285 [nxp_nci_i2c]
     ? preempt_count_add+0x68/0xa0
     ? irq_forced_thread_fn+0x80/0x80
     irq_thread_fn+0x20/0x60
     irq_thread+0xee/0x180
     ? wake_threads_waitq+0x30/0x30
     kthread+0xfb/0x130
     ? irq_thread_check_affinity+0xd0/0xd0
     ? kthread_park+0x90/0x90
     ret_from_fork+0x1f/0x40

Afterward the kernel must be rebooted to work properly again.

This happens because it attempts to call nci_recv_frame() with skb == NULL.
However, unlike nxp_nci_fw_recv_frame(), nci_recv_frame() does not have any
NULL checks for skb, causing the NULL pointer dereference.

Change the code to call only nxp_nci_fw_recv_frame() in case of an error.
Make sure to log it so it is obvious that a communication error occurred.
The error above then becomes:

    nxp-nci_i2c i2c-NXP1001:00: NFC: Read failed with error -121
    nci: __nci_request: wait_for_completion_interruptible_timeout failed 0
    nxp-nci_i2c i2c-NXP1001:00: NFC: Read failed with error -121

Fixes: 6be88670 ("NFC: nxp-nci_i2c: Add I2C support to NXP NCI driver")
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/nfc/nxp-nci/i2c.c

@@ -220,8 +220,10 @@ static irqreturn_t nxp_nci_i2c_irq_thread_fn(int irq, void *phy_id)
 
 	if (r == -EREMOTEIO) {
 		phy->hard_fault = r;
-		skb = NULL;
-	} else if (r < 0) {
+		if (info->mode == NXP_NCI_MODE_FW)
+			nxp_nci_fw_recv_frame(phy->ndev, NULL);
+	}
+	if (r < 0) {
 		nfc_err(&client->dev, "Read failed with error %d\n", r);
 		goto exit_irq_handled;
 	}