Fixing a bug in tests/tagged_terminal.cpp
Fixing a bug in tests/tagged_terminal.cpp

Slices should be used with single compute device.

Poulpy21/vexcl,ddemidov/vexcl,Poulpy21/vexcl,kapadia/vexcl,kapadia/vexcl,ddemidov/vexcl,Poulpy21/vexcl