wifi: rt2x00: Switch to use hrtimer_update_function()

The field 'function' of struct hrtimer should not be changed directly, as
the write is lockless and a concurrent timer expiry might end up using the
wrong function pointer.

Switch to use hrtimer_update_function() which also performs runtime checks
that it is safe to modify the callback.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/82dcc0eae40bb84e6452f242751c0650e79bd87e.1738746927.git.namcao@linutronix.de

drivers/net/wireless/ralink/rt2x00/rt2800mmio.c

@@ -842,7 +842,7 @@ int rt2800mmio_probe_hw(struct rt2x00_dev *rt2x00dev)
 	/*
 	 * Set txstatus timer function.
 	 */
-	rt2x00dev->txstatus_timer.function = rt2800mmio_tx_sta_fifo_timeout;
+	hrtimer_update_function(&rt2x00dev->txstatus_timer, rt2800mmio_tx_sta_fifo_timeout);
 
 	/*
 	 * Overwrite TX done handler

drivers/net/wireless/ralink/rt2x00/rt2800usb.c

@@ -618,7 +618,7 @@ static int rt2800usb_probe_hw(struct rt2x00_dev *rt2x00dev)
 	/*
 	 * Set txstatus timer function.
 	 */
-	rt2x00dev->txstatus_timer.function = rt2800usb_tx_sta_fifo_timeout;
+	hrtimer_update_function(&rt2x00dev->txstatus_timer, rt2800usb_tx_sta_fifo_timeout);
 
 	/*
 	 * Overwrite TX done handler