constify rw_verify_area()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/internal.h b/fs/internal.h
index f6ad343..7c5f01c 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -131,6 +131,7 @@
  * read_write.c
  */
 extern ssize_t __kernel_write(struct file *, const char *, size_t, loff_t *);
+extern int rw_verify_area(int, struct file *, const loff_t *, size_t);
 
 /*
  * splice.c