sparc64: do not export pus_fs_struct

Al asked: BTW, why does sparc64 export put_fs_struct?  Grepping the
kernel tree did not show any users of an exported put_fs_struct - so
drop the export.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>