linux-generic: fix alignment of struct stat/statfs for nios2

linux-generic: fix alignment of struct stat/statfs for nios2

The hard alignment of 8 was appropriate for most platforms for
which 8-byte values are 8-byte aligned, but this is not true
for the nios2 platform, so only align to the alignment of the
8-byte type on the platform.

Remove the explicit alignment of struct statfs as it's redundant.