[SPARC64]: check fork_idle() error

Check the return value of fork_idle() to catch error.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc64/kernel/smp.c b/arch/sparc64/kernel/smp.c
index b84c49e..c73b7a4 100644
--- a/arch/sparc64/kernel/smp.c
+++ b/arch/sparc64/kernel/smp.c
@@ -353,6 +353,8 @@
 	int timeout, ret;
 
 	p = fork_idle(cpu);
+	if (IS_ERR(p))
+		return PTR_ERR(p);
 	callin_flag = 0;
 	cpu_new_thread = task_thread_info(p);