Staging: wlags49_h2: add missing <linux/string.h> for strlen

On ia64, the build fails with incompatible implicit definition of strlen.
This patch adds the <linux/string.h> include to get the real prototype.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/wlags49_h2/wl_enc.c

@@ -62,6 +62,7 @@
 /*******************************************************************************
  *  include files
  ******************************************************************************/
+#include <linux/string.h>
 #include <wl_version.h>
 
 #include <debug.h>