trace: Properly return the print_line_t value

The current function trace_graph_ret_raw has
an unreachable statement. This leads to the wrong
return value in some situations. This can be fixed
by modifying the control flow statements. Namely
the if statement with an empty body.

Change-Id: I1f621171661caa57a3e759449bfda432088530d6
Signed-off-by: Clyde Byrd III <cbyrd@codeaurora.org>