[PATCH] I2C: fix Hangs with w83781d

Here is a patch for the w83781d driver that prevents register bits from
being arbitrary changed when we force temp2/3 to comparator mode. Keith
Duthie had been reporting various problems with that driver and finally
found that this arbitrary change was the cause of them. He also tested
this patch, which he confirmed to work.

drivers/i2c/chips/w83781d.c

@@ -1632,7 +1632,11 @@ w83781d_init_client(struct i2c_client *client)
 		if (type != w83781d) {
 			/* enable comparator mode for temp2 and temp3 so
 			   alarm indication will work correctly */
-			w83781d_write_value(client, W83781D_REG_IRQ, 0x41);
+			i = w83781d_read_value(client, W83781D_REG_IRQ);
+			if (!(i & 0x40))
+				w83781d_write_value(client, W83781D_REG_IRQ,
+						    i | 0x40);
+
 			for (i = 0; i < 3; i++)
 				data->pwmenable[i] = 1;
 		}