fs/ntfs3: Fix wrong cast in xattr.c

cpu_to_be32 and be32_to_cpu respectively return and receive
__be32, change the cast to the correct types.

Fixes the following sparse warnings:
fs/ntfs3/xattr.c:811:48: sparse: sparse: incorrect type in
                         assignment (different base types)
fs/ntfs3/xattr.c:901:34: sparse: sparse: cast to restricted __be32

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Daniel Pinto <danielpinto52@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>