Bugfix: Fix cl_ext.h include path in CL backend
Bugfix: Fix cl_ext.h include path in CL backend

Signed-off-by: Francis Murtagh <e59f6df1240b2b6c2b05aa682b1b9d01b9505720@arm.com>
Change-Id: I560c9f6297e9552bab26a6f88765830409be78c3

ARM-software/armnn,ARM-software/armnn,ARM-software/armnn