kernel/fork.c: remove duplicated include

Remove duplicated include.

Link: http://lkml.kernel.org/r/20181209062952.17736-1-yuehaibing@huawei.comSigned-off-by: NYueHaibing <yuehaibing@huawei.com>
Reviewed-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

@@ -77,7 +77,6 @@
 #include <linux/blkdev.h>
 #include <linux/fs_struct.h>
 #include <linux/magic.h>
-#include <linux/sched/mm.h>
 #include <linux/perf_event.h>
 #include <linux/posix-timers.h>
 #include <linux/user-return-notifier.h>