libnvdimm: remove duplicate include

Removed duplicate include.
Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/nd-core.h

@@ -14,7 +14,6 @@
 #define __ND_CORE_H__
 #include <linux/libnvdimm.h>
 #include <linux/device.h>
-#include <linux/libnvdimm.h>
 #include <linux/sizes.h>
 #include <linux/mutex.h>
 #include <linux/nd.h>