missing export of csum_partial() on uml/amd64

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/sys-x86_64/ksyms.c

-#include "linux/module.h"
-#include "asm/string.h"
+#include <linux/module.h>
+#include <asm/string.h>
+#include <asm/checksum.h>
 
 /*XXX: we need them because they would be exported by x86_64 */
 EXPORT_SYMBOL(__memcpy);
+EXPORT_SYMBOL(csum_partial);