Uninitialized timespec fields in stat

[FrankHB]

This commit removed some redundant assignments on implementation-specific fields. However, it also left some public ones uninitialized.

Probably adding this would be better:

st->st_atim.tv_nsec = 0;
st->st_mtim.tv_nsec = 0;
st->st_ctim.tv_nsec = 0;