Bluetooth: hci_ll: Replace mdelay with msleep in download_firmware

download_firmware() is never called from atomic context.

It is only called by ll_setup() that is called only via function pointer
"->setup" used in hci_uart_setup() in drivers/bluetooth/hci_serdev.c and
drivers/bluetooth/hci_ldisc.c. hci_uart_setup() is called only
via function pointer "->setup" used in hci_dev_do_open()
in net/bluetooth/hci_core.c.
All of the above functions do not enter atomic context.

Besides, ll_setup() calls msleep() and hci_dev_do_open calls mutex_lock().
So it indicates that all the above functions call functions that can sleep.

Despite never getting called from atomic context, download_firmware()
calls mdelay() for busy wait.
That is not necessary and can be replaced with msleep to avoid busy wait.

This is found by a static analysis tool named DCNS written by myself.
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ll.c

@@ -650,7 +650,7 @@ static int download_firmware(struct ll_device *lldev)
 			break;
 		case ACTION_DELAY:	/* sleep */
 			bt_dev_info(lldev->hu.hdev, "sleep command in scr");
-			mdelay(((struct bts_action_delay *)action_ptr)->msec);
+			msleep(((struct bts_action_delay *)action_ptr)->msec);
 			break;
 		}
 		len -= (sizeof(struct bts_action) +