btrfs: extent-tree: Open-code process_func in __btrfs_mod_ref

The process_func function pointer is local to __btrfs_mod_ref() and
points to either btrfs_inc_extent_ref() or btrfs_free_extent().

Open code it to make later delayed ref refactor easier, so we can
refactor btrfs_inc_extent_ref() and btrfs_free_extent() in different
patches.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -3157,10 +3157,6 @@ static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
 	int i;
 	int level;
 	int ret = 0;
-	int (*process_func)(struct btrfs_trans_handle *,
-			    struct btrfs_root *,
-			    u64, u64, u64, u64, u64, u64);
-
 
 	if (btrfs_is_testing(fs_info))
 		return 0;
@@ -3172,11 +3168,6 @@ static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
 	if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state) && level == 0)
 		return 0;
 
-	if (inc)
-		process_func = btrfs_inc_extent_ref;
-	else
-		process_func = btrfs_free_extent;
-
 	if (full_backref)
 		parent = buf->start;
 	else
@@ -3198,16 +3189,27 @@ static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
 
 			num_bytes = btrfs_file_extent_disk_num_bytes(buf, fi);
 			key.offset -= btrfs_file_extent_offset(buf, fi);
-			ret = process_func(trans, root, bytenr, num_bytes,
-					   parent, ref_root, key.objectid,
-					   key.offset);
+			if (inc)
+				ret = btrfs_inc_extent_ref(trans, root, bytenr,
+						num_bytes, parent, ref_root,
+						key.objectid, key.offset);
+			else
+				ret = btrfs_free_extent(trans, root, bytenr,
+						num_bytes, parent, ref_root,
+						key.objectid, key.offset);
 			if (ret)
 				goto fail;
 		} else {
 			bytenr = btrfs_node_blockptr(buf, i);
 			num_bytes = fs_info->nodesize;
-			ret = process_func(trans, root, bytenr, num_bytes,
-					   parent, ref_root, level - 1, 0);
+			if (inc)
+				ret = btrfs_inc_extent_ref(trans, root, bytenr,
+						num_bytes, parent, ref_root,
+						level - 1, 0);
+			else
+				ret = btrfs_free_extent(trans, root, bytenr,
+						num_bytes, parent, ref_root,
+						level - 1, 0);
 			if (ret)
 				goto fail;
 		}