Silence warnings

Silence warnings

The following warnings are fixed by this:

 hantek_6022be.c:424: warning 158: overflow in implicit constant conversion
 sainsmart_dds120.c:359: warning 158: overflow in implicit constant conversion
 sainsmart_dds120.c:363: warning 158: overflow in implicit constant conversion
 sainsmart_dds120.c:366: warning 158: overflow in implicit constant conversion
 sainsmart_dds120.c:370: warning 158: overflow in implicit constant conversion
 sainsmart_dds120.c:494: warning 158: overflow in implicit constant conversion