Tidy up code to determine bit mask for ballot scans (#1363)
Tidy up code to determine bit mask for ballot scans (#1363)

It seems more intuitive to set only the bits that are required, rather
than to set one more bit than is required, only to clear it again.

Signed-off-by: Stuart Brady <5927b716ca6102ab3dc7740efab72ff15951354e@arm.com>
KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS