platform/x86: thinkpad_acpi: take mutex for hotkey_mask_{set,get}

hotkey_mask_set() and hotkey_mask_get() expect hotkey_mutex to be held.
While it should not matter during initialization a following patch will
enable lockdep for hotkey_mutex which would produce warnings here.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20230704-thinkpad_acpi-lockdep-v1-1-60129548a738@weissschuh.net
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -3478,7 +3478,9 @@ static int __init hotkey_init(struct ibm_init_struct *iibm)
 	if (tp_features.hotkey_mask) {
 		/* hotkey_source_mask *must* be zero for
 		 * the first hotkey_mask_get to return hotkey_orig_mask */
+		mutex_lock(&hotkey_mutex);
 		res = hotkey_mask_get();
+		mutex_unlock(&hotkey_mutex);
 		if (res)
 			return res;
 
@@ -3577,9 +3579,11 @@ static int __init hotkey_init(struct ibm_init_struct *iibm)
 		hotkey_exit();
 		return res;
 	}
+	mutex_lock(&hotkey_mutex);
 	res = hotkey_mask_set(((hotkey_all_mask & ~hotkey_reserved_mask)
 			       | hotkey_driver_mask)
 			      & ~hotkey_source_mask);
+	mutex_unlock(&hotkey_mutex);
 	if (res < 0 && res != -ENXIO) {
 		hotkey_exit();
 		return res;