staging: wfx: remove remaining code of 'secure link' feature

Commit e8d607ce ("staging: wfx: drop 'secure link' feature") had
removed the 'secure link' feature. However, a few lines of codes were
yet here.

Fixes: e8d607ce ("staging: wfx: drop 'secure link' feature")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20201007101943.749898-3-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/Documentation/devicetree/bindings/net/wireless/siliabs,wfx.txt

@@ -90,8 +90,6 @@ Some properties are recognized either by SPI and SDIO versions:
    this property, driver will disable most of power saving features.
  - config-file: Use an alternative file as PDS. Default is `wf200.pds`. Only
    necessary for development/debug purpose.
- - slk_key: String representing hexadecimal value of secure link key to use.
-   Must contains 64 hexadecimal digits. Not supported in current version.
 
 WFx driver also supports `mac-address` and `local-mac-address` as described in
 Documentation/devicetree/bindings/net/ethernet.txt

drivers/staging/wfx/debug.c

@@ -230,21 +230,6 @@ static const struct file_operations wfx_send_pds_fops = {
 	.write = wfx_send_pds_write,
 };
 
-static ssize_t wfx_burn_slk_key_write(struct file *file,
-				      const char __user *user_buf,
-				      size_t count, loff_t *ppos)
-{
-	struct wfx_dev *wdev = file->private_data;
-
-	dev_info(wdev->dev, "this driver does not support secure link\n");
-	return -EINVAL;
-}
-
-static const struct file_operations wfx_burn_slk_key_fops = {
-	.open = simple_open,
-	.write = wfx_burn_slk_key_write,
-};
-
 struct dbgfs_hif_msg {
 	struct wfx_dev *wdev;
 	struct completion complete;
@@ -366,8 +351,6 @@ int wfx_debug_init(struct wfx_dev *wdev)
 	debugfs_create_file("tx_power_loop", 0444, d, wdev,
 			    &wfx_tx_power_loop_fops);
 	debugfs_create_file("send_pds", 0200, d, wdev, &wfx_send_pds_fops);
-	debugfs_create_file("burn_slk_key", 0200, d, wdev,
-			    &wfx_burn_slk_key_fops);
 	debugfs_create_file("send_hif_msg", 0600, d, wdev,
 			    &wfx_send_hif_msg_fops);
 	debugfs_create_file("ps_timeout", 0600, d, wdev, &wfx_ps_timeout_fops);