misc/pvpanic: Make some symbols static

Fix sparse warnings:

drivers/misc/pvpanic/pvpanic.c:28:18: warning:
 symbol 'pvpanic_list' was not declared. Should it be static?
drivers/misc/pvpanic/pvpanic.c:29:12: warning:
 symbol 'pvpanic_lock' was not declared. Should it be static?
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20210331121706.15268-1-yuehaibing@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/pvpanic/pvpanic.c

@@ -25,8 +25,8 @@ MODULE_AUTHOR("Mihai Carabas <mihai.carabas@oracle.com>");
 MODULE_DESCRIPTION("pvpanic device driver ");
 MODULE_LICENSE("GPL");
 
-struct list_head pvpanic_list;
-spinlock_t pvpanic_lock;
+static struct list_head pvpanic_list;
+static spinlock_t pvpanic_lock;
 
 static void
 pvpanic_send_event(unsigned int event)