wl12xx: alloc buffer in driver_state_read to prevent compilation warning

When compiling wl12xx for x86, there was a warning complaining about
the size of the buffer we were allocating in the stack:

drivers/net/wireless/wl12xx/debugfs.c: In function 'driver_state_read':
drivers/net/wireless/wl12xx/debugfs.c:380:1: warning: the frame size of 1040 bytes is larger than 1024 bytes

To prevent this, allocate the buffer in the heap instead.
Signed-off-by: Luciano Coelho <coelho@ti.com>

drivers/net/wireless/wl12xx/debugfs.c

@@ -317,12 +317,19 @@ static ssize_t driver_state_read(struct file *file, char __user *user_buf,
 {
 	struct wl1271 *wl = file->private_data;
 	int res = 0;
-	char buf[1024];
+	ssize_t ret;
+	char *buf;
+
+#define DRIVER_STATE_BUF_LEN 1024
+
+	buf = kmalloc(DRIVER_STATE_BUF_LEN, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
 
 	mutex_lock(&wl->mutex);
 
 #define DRIVER_STATE_PRINT(x, fmt)   \
-	(res += scnprintf(buf + res, sizeof(buf) - res,\
+	(res += scnprintf(buf + res, DRIVER_STATE_BUF_LEN - res,\
 			  #x " = " fmt "\n", wl->x))
 
 #define DRIVER_STATE_PRINT_LONG(x) DRIVER_STATE_PRINT(x, "%ld")
@@ -373,10 +380,13 @@ static ssize_t driver_state_read(struct file *file, char __user *user_buf,
 #undef DRIVER_STATE_PRINT_LHEX
 #undef DRIVER_STATE_PRINT_STR
 #undef DRIVER_STATE_PRINT
+#undef DRIVER_STATE_BUF_LEN
 
 	mutex_unlock(&wl->mutex);
 
-	return simple_read_from_buffer(user_buf, count, ppos, buf, res);
+	ret = simple_read_from_buffer(user_buf, count, ppos, buf, res);
+	kfree(buf);
+	return ret;
 }
 
 static const struct file_operations driver_state_ops = {