Fix compilation failure with -Werror=narrowing (#901)
Fix compilation failure with -Werror=narrowing (#901)

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