fs/ntfs3: Missed le32_to_cpu conversion

NTFS data structure fields are stored in little-endian, it is necessary
to take this into account when working on big-endian architectures.

Fixes: 1b7dd28e("fs/ntfs3: Correct function is_rst_area_valid")
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>