mips/cpu: Make sure play_dead() doesn't return

play_dead() doesn't return.  Make that more explicit with a BUG().

BUG() is preferable to unreachable() because BUG() is a more explicit
failure mode and avoids undefined behavior like falling off the edge of
the function into whatever code happens to be next.
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/b195e4da190bb06b7d4af15d66ce6129e2347630.1676358308.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

arch/mips/kernel/smp-bmips.c

@@ -415,6 +415,8 @@ void __ref play_dead(void)
 	"	wait\n"
 	"	j	bmips_secondary_reentry\n"
 	: : : "memory");
+
+	BUG();
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */

arch/mips/loongson64/smp.c

@@ -823,6 +823,7 @@ void play_dead(void)
 	state_addr = &per_cpu(cpu_state, cpu);
 	mb();
 	play_dead_at_ckseg1(state_addr);
+	BUG();
 }
 
 static int loongson3_disable_clock(unsigned int cpu)