PPC32: rearrange includes in arch/ppc/kernel/irq.c to fix a compile error.

arch/ppc/kernel/irq.c

@@ -29,13 +29,12 @@
  * to reduce code space and undefined function references.
  */
 
-
-#include <linux/ptrace.h>
 #include <linux/errno.h>
 #include <linux/threads.h>
 #include <linux/kernel_stat.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
+#include <linux/ptrace.h>
 #include <linux/ioport.h>
 #include <linux/interrupt.h>
 #include <linux/timex.h>