Fix zfs_getattr_fast types

Fix zfs_getattr_fast types

On Sparc sp->blksize will be a 64-bit value which is then cast
incorrectly to a 32-bit value.  For big endian systems this
results in an incorrect value for sp->blksize.  To resolve the
problem local variables of the correct size are used and then
assigned to sp->blksize.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: marku89 <mar42@kola.li>
Issue #1700