Libocl: Fix get_sub_group_size bug
Libocl: Fix get_sub_group_size bug

If last sub group has the max sub group size, it will return 0 instead
of max sub group size. Fix the bug.
V2: Remove useless check for threadn, threadn should always bigger than 1.

Signed-off-by: Pan Xiuli <e5a665b1e626c5dc0826076a8b5a209eb48bf6ee@intel.com>
Reviewed-by: Yang Rong <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet