btrfs: qgroup: Cleanup old inaccurate facilities

Cleanup the old facilities which use old btrfs_qgroup_reserve() function
call, replace them with the newer version, and remove the "__" prefix in
them.

Also, make btrfs_qgroup_reserve/free() functions private, as they are
now only used inside qgroup codes.

Now, the whole btrfs qgroup is swithed to use the new reserve facilities.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 70732e6..7ed033a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1119,7 +1119,7 @@
 
 	page_cnt = min_t(u64, (u64)num_pages, (u64)file_end - start_index + 1);
 
-	ret = __btrfs_delalloc_reserve_space(inode,
+	ret = btrfs_delalloc_reserve_space(inode,
 			start_index << PAGE_CACHE_SHIFT,
 			page_cnt << PAGE_CACHE_SHIFT);
 	if (ret)
@@ -1210,7 +1210,7 @@
 		spin_lock(&BTRFS_I(inode)->lock);
 		BTRFS_I(inode)->outstanding_extents++;
 		spin_unlock(&BTRFS_I(inode)->lock);
-		__btrfs_delalloc_release_space(inode,
+		btrfs_delalloc_release_space(inode,
 				start_index << PAGE_CACHE_SHIFT,
 				(page_cnt - i_done) << PAGE_CACHE_SHIFT);
 	}
@@ -1237,7 +1237,7 @@
 		unlock_page(pages[i]);
 		page_cache_release(pages[i]);
 	}
-	__btrfs_delalloc_release_space(inode,
+	btrfs_delalloc_release_space(inode,
 			start_index << PAGE_CACHE_SHIFT,
 			page_cnt << PAGE_CACHE_SHIFT);
 	return ret;