sh: Replace an explicit computation by the use of the container_of macro

The macro container_of from kernel.h performs the same
pointer arithmetic operation.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
type T;
expression mptr;
expression member;
@@

- (void *)((char *)mptr - offsetof(T, member))
+ container_of(mptr, T, member)
// </smpl>
Signed-off-by: Nicolas Palix <npalix@diku.dk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/cpu/irq/ipr.c

@@ -17,16 +17,17 @@
  * for more details.
  */
 #include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
 #include <linux/irq.h>
+#include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/io.h>
-#include <linux/interrupt.h>
 #include <linux/topology.h>
 
 static inline struct ipr_desc *get_ipr_desc(unsigned int irq)
 {
 	struct irq_chip *chip = get_irq_chip(irq);
-	return (void *)((char *)chip - offsetof(struct ipr_desc, chip));
+	return container_of(chip, struct ipr_desc, chip);
 }
 
 static void disable_ipr_irq(unsigned int irq)