riscv: remove unreachable !HAVE_FUNCTION_GRAPH_RET_ADDR_PTR code

HAVE_FUNCTION_GRAPH_RET_ADDR_PTR is always defined for RISC-V.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/stacktrace.c

@@ -64,12 +64,8 @@ static void notrace walk_stackframe(struct task_struct *task,
 		frame = (struct stackframe *)fp - 1;
 		sp = fp;
 		fp = frame->fp;
-#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 		pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
 					   (unsigned long *)(fp - 8));
-#else
-		pc = frame->ra - 0x4;
-#endif
 	}
 }