constify get_dcookie() and friends

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index 82f7000..642478d 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -206,7 +206,7 @@
  * because we cannot reach this code without at least one
  * dcookie user still being registered (namely, the reader
  * of the event buffer). */
-static inline unsigned long fast_get_dcookie(struct path *path)
+static inline unsigned long fast_get_dcookie(const struct path *path)
 {
 	unsigned long cookie;