fs: inode.c use atomic_inc_return in __iget

Using atomic_inc_return in __iget(struct inode *inode) makes the intent
of this code clearer and generates less code on processors that have
this operation.

On x86_64 this patch reduces the text size of inode.o by 12 bytes.
Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>

----
patch against 2.6.34-rc7
compiled & tested on x86_64 AMD X2

I've been running with this patch applied for several weeks with no
obvious problems.
regards
Richard
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/inode.c

@@ -286,11 +286,9 @@ static void init_once(void *foo)
  */
 void __iget(struct inode *inode)
 {
-	if (atomic_read(&inode->i_count)) {
-		atomic_inc(&inode->i_count);
+	if (atomic_inc_return(&inode->i_count) != 1)
 		return;
-	}
-	atomic_inc(&inode->i_count);
+
 	if (!(inode->i_state & (I_DIRTY|I_SYNC)))
 		list_move(&inode->i_list, &inode_in_use);
 	inodes_stat.nr_unused--;