mtip32xx: restrict variables visible in current code module

The modified variables are only used in the file mtip32xx.c.
As such, the static keyword is inserted to define that object
to be only visible to the current code module during compilation.
Signed-off-by: NZhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/block/mtip32xx/mtip32xx.c

@@ -104,9 +104,9 @@
 /* Device instance number, incremented each time a device is probed. */
 static int instance;
 
-struct list_head online_list;
-struct list_head removing_list;
-spinlock_t dev_lock;
+static struct list_head online_list;
+static struct list_head removing_list;
+static spinlock_t dev_lock;
 
 /*
  * Global variable used to hold the major block device number