tracing/branch-tracer: include missing irqflags.h

Impact: fix build error on branch tracer

This should fix a build error reported on alpha in linux-next:

 CC      kernel/trace/trace_branch.o
  kernel/trace/trace_branch.c: In function 'probe_likely_condition':
  kernel/trace/trace_branch.c:44: error: implicit declaration of function 'raw_local_irq_save'
  kernel/trace/trace_branch.c:76: error: implicit declaration of function 'raw_local_irq_restore'

Unfortunately, I can't test it since I don't have any Alpha build environment.
Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_branch.c

@@ -6,6 +6,7 @@
 #include <linux/kallsyms.h>
 #include <linux/seq_file.h>
 #include <linux/spinlock.h>
+#include <linux/irqflags.h>
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/module.h>