btrfs: Remove redundant tree argument from extent_readpages

This function is called only from btrfs_readpage and is already passed
the mapping. Simplify its signature by moving the code obtaining
reference to the extent tree in the function. No functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 29d47383b..752ad87 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -416,9 +416,8 @@ int extent_writepages(struct extent_io_tree *tree,
 		      struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
 			    struct writeback_control *wbc);
-int extent_readpages(struct extent_io_tree *tree,
-		     struct address_space *mapping,
-		     struct list_head *pages, unsigned nr_pages);
+int extent_readpages(struct address_space *mapping, struct list_head *pages,
+		     unsigned nr_pages);
 int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		__u64 start, __u64 len);
 void set_page_extent_mapped(struct page *page);