cw1200: remove duplicated include from wsm.c

Remove duplicated include.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/cw1200/wsm.c

@@ -12,7 +12,6 @@
 
 #include <linux/skbuff.h>
 #include <linux/wait.h>
-#include <linux/skbuff.h>
 #include <linux/delay.h>
 #include <linux/sched.h>
 #include <linux/random.h>