ext4: do not interpret high bytes if 64bit feature is disabled

Fields s_free_blocks_count_hi, s_r_blocks_count_hi and s_blocks_count_hi
are not valid if EXT4_FEATURE_INCOMPAT_64BIT is not enabled and should be
treated as zeroes.

Signed-off-by: Petr Malat <oss@malat.biz>
Link: https://lore.kernel.org/r/20200825150016.3363-1-oss@malat.biz


Signed-off-by: Theodore Ts'o <tytso@mit.edu>