ggml : return input tensor in ggml_set_name (#262)

ggml : return input tensor in ggml_set_name (#262)

this is SO USEFUL for debugging. in order to find any cgraph node,
I can wrap it in ggml_set_name and set a conditional breakpoint.

but I can only wrap existing code if this returns its input.
otherwise the barrier becomes annoyingly high (have to move a
bunch of code around to add name to a tensor)