ntfstruncate.c: Fix mixed endianness usage of variable 'u'.

ntfstruncate.c: Fix mixed endianness usage of variable 'u'.

In 'dump_attr_record' the variable 'u' was first used to store a
CPU-endian 32-bit value, and then to store a 16-bit little-endian value.
This is bad practice and results in a hard error when strict endian type
checking is used.

Fixed by storing the 16-bit little-endian flags value in a new variable
'flags'.