Set the default grid size to valid value
Set the default grid size to valid value

For 1-dimensional grids the grid size is reduced to 2^15 (instead of
65536 = 2^16), because current GPUs do not support grids with a first dimension
larger than 65535 = 2^16 - 1.

Signed-off-by: Tobias Grosser <059b8b880f8441509ec8a65b50b4c6ae74ebea76@grosser.es>
Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

nicolasvasilache/ppcg,Meinersbur/ppcg,Meinersbur/ppcg,nicolasvasilache/ppcg