btrfs: Remove extra parentheses from condition in copy_items()

There is no need for the extra pair of parentheses, remove it. This
fixes the following warning when building with clang:

fs/btrfs/tree-log.c:3694:10: warning: equality comparison with extraneous
  parentheses [-Wparentheses-equality]
                if ((i == (nr - 1)))
                     ~~^~~~~~~~~~~

Also remove the unnecessary parentheses around the substraction.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -3688,7 +3688,7 @@ static noinline int copy_items(struct btrfs_trans_handle *trans,
 
 		src_offset = btrfs_item_ptr_offset(src, start_slot + i);
 
-		if ((i == (nr - 1)))
+		if (i == nr - 1)
 			last_key = ins_keys[i];
 
 		if (ins_keys[i].type == BTRFS_INODE_ITEM_KEY) {