blockconsole: Fix undefined MAX_RT_PRIO

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/drivers/block/blockconsole.c b/drivers/block/blockconsole.c
index e88b8ee..c22272f 100644
--- a/drivers/block/blockconsole.c
+++ b/drivers/block/blockconsole.c
@@ -16,6 +16,7 @@
 #include <linux/string.h>
 #include <linux/workqueue.h>
 #include <linux/sched.h>
+#include <linux/sched/rt.h>
 #include <linux/ctype.h>
 
 #define BLOCKCONSOLE_MAGIC	"\nLinux blockconsole version 1.1\n"