Fix problem in elpa2_print_kernels with GPU kernel
The GPU kernel can only be set, if e%set("use_gpu",1) has been set before and GPU usage was thus requested.
In the elpa2_print_kernels, this was not reflected, and the GPU kernels were checked via can_set method without activating GPU usage => GPU kernels were always reported as non exisitent
Edited by Andreas Marek