net: Drop duplicate include of dm.h in pcnet.c

This file includes the header twice. Drop the second one.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/net/pcnet.c

@@ -10,7 +10,6 @@
 #include <cpu_func.h>
 #include <dm.h>
 #include <log.h>
-#include <dm.h>
 #include <malloc.h>
 #include <memalign.h>
 #include <net.h>