media: dvb-frontends/mxl5xx: declare LIST_HEAD(mxllist) static

Fixes one sparse warning:
  mxl5xx.c:46:1: warning: symbol 'mxllist' was not declared. Should it be static?
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/dvb-frontends/mxl5xx.c

@@ -43,7 +43,7 @@
 #define BYTE2(v) ((v >> 16) & 0xff)
 #define BYTE3(v) ((v >> 24) & 0xff)
 
-LIST_HEAD(mxllist);
+static LIST_HEAD(mxllist);
 
 struct mxl_base {
 	struct list_head     mxllist;