ipw2100: mark ipw2100_pm_qos_req static

  CHECK   drivers/net/wireless/ipw2x00/ipw2100.c
drivers/net/wireless/ipw2x00/ipw2100.c:177:28: warning: symbol 'ipw2100_pm_qos_req' was not declared. Should it be static?
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ipw2x00/ipw2100.c

@@ -174,7 +174,7 @@ that only one external action is invoked at a time.
 #define DRV_DESCRIPTION	"Intel(R) PRO/Wireless 2100 Network Driver"
 #define DRV_COPYRIGHT	"Copyright(c) 2003-2006 Intel Corporation"
 
-struct pm_qos_request_list *ipw2100_pm_qos_req;
+static struct pm_qos_request_list *ipw2100_pm_qos_req;
 
 /* Debugging stuff */
 #ifdef CONFIG_IPW2100_DEBUG