x86/mm, mm/hwpoison: Fix the unmap kernel 1:1 pages check condition

When fd0e786d9d09 ("x86/mm, mm/hwpoison: Don't unconditionally unmap
kernel 1:1 pages") was backported to 4.14.y, the logic was reversed when
calling memory_failure() to determine whether it needs to unmap the
kernel page. Only when memory_failure() returns successfully, the kernel
page can be unmapped.

Signed-off-by: luofei <luofei@unicloud.com>
Cc: stable@vger.kernel.org #v4.14.x
Cc: stable@vger.kernel.org #v4.15.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>