fs/read_write.c: fix generic_file_llseek() comment

Commit ef3d0fd2 ("vfs: do (nearly) lockless generic_file_llseek")
has removed i_mutex from generic_file_llseek, so update the comment
accordingly.
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/read_write.c

@@ -128,7 +128,7 @@ EXPORT_SYMBOL(generic_file_llseek_size);
  *
  * This is a generic implemenation of ->llseek useable for all normal local
  * filesystems.  It just updates the file offset to the value specified by
- * @offset and @whence under i_mutex.
+ * @offset and @whence.
  */
 loff_t generic_file_llseek(struct file *file, loff_t offset, int whence)
 {