hantek-4032l: Fix structure packing.

hantek-4032l: Fix structure packing.

- use pragma to handle different behavior between gcc and minGW bit-field packing
- bit-field integer variables needs to be align to 2-byte boundary
Compiler does not produce an error when accessing into non-__packed pointer.
However, the field might not be properly aligned for this type.
More information could be found on:
 - https://sourceforge.net/p/mingw-w64/bugs/275/
 - http://www.keil.com/support/man/docs/ARMCC/armcc_chr1359124990875.htm

Signed-off-by: Andrej Valek <redacted>