[media] dvb_usb_core: fix sparse warning

drivers/media/usb/dvb-usb-v2/dvb_usb_core.c:24:5: warning: symbol 'dvb_usbv2_disable_rc_polling' was not declared. Should it be static?
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/dvb-usb-v2/dvb_usb_core.c

@@ -21,7 +21,7 @@
 
 #include "dvb_usb_common.h"
 
-int dvb_usbv2_disable_rc_polling;
+static int dvb_usbv2_disable_rc_polling;
 module_param_named(disable_rc_polling, dvb_usbv2_disable_rc_polling, int, 0644);
 MODULE_PARM_DESC(disable_rc_polling,
 		"disable remote control polling (default: 0)");