caif: remove duplicated include

Remove duplicated include.
Signed-off-by: Nicolas Kaiser <nikai@nikai.net>
Acked-by: Sjur Braendeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/caif/caif_socket.c

@@ -17,7 +17,6 @@
 #include <linux/poll.h>
 #include <linux/tcp.h>
 #include <linux/uaccess.h>
-#include <linux/mutex.h>
 #include <linux/debugfs.h>
 #include <linux/caif/caif_socket.h>
 #include <asm/atomic.h>