Fix typo in README
Fix typo in README

Signed-off-by: Kevin Petit <9b79a2d3df4408bbf6fcf0c9904434a8637f93cf@arm.com>

KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS,KhronosGroup/OpenCL-CTS