sh: unbreak WARN_ON()

Fix WARN_ON() by modifying the bug trap handling code to
always return in the in-kernel instruction pointer case.
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/traps.c

@@ -69,6 +69,7 @@ BUILD_TRAP_HANDLER(bug)
 		insn_size_t insn = *(insn_size_t *)instruction_pointer(regs);
 		if (insn == TRAPA_BUG_OPCODE)
 			handle_BUG(regs);
+		return;
 	}
 #endif