kerndat: munmap when stat call fail
kerndat: munmap when stat call fail

Avoid memleak in err case

Signed-off-by: Libo Chen <03ac321f4fc44d5558b43fe86a753e021008f32d@huawei.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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