staging: wilc1000: fix sparse warning: symbol was not declared. Should it be static?

- Fixed a sparse warning:
  wilc_debugfs.c:32:10: warning: symbol 'WILC_DEBUG_LEVEL' was not declared. Should it be static?
Signed-off-by: Matias Mucciolo <mmucciolo@suteba.org.ar>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/wilc_debugfs.c

@@ -29,7 +29,7 @@ static struct dentry *wilc_dir;
 #define ERR             BIT(3)
 
 #define DBG_LEVEL_ALL	(DEBUG | INFO | WRN | ERR)
-atomic_t WILC_DEBUG_LEVEL = ATOMIC_INIT(ERR);
+static atomic_t WILC_DEBUG_LEVEL = ATOMIC_INIT(ERR);
 EXPORT_SYMBOL_GPL(WILC_DEBUG_LEVEL);
 
 /*