btrfs: use variable for io_tree when clearing range in btrfs_page_mkwrite()

We have the inode's io_tree already stored in a local variable, so use it
instead of grabbing it again in the call to btrfs_clear_extent_bit().

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/file.c

@@ -1950,7 +1950,7 @@ static vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
 	 * clear any delalloc bits within this page range since we have to
 	 * reserve data&meta space before lock_page() (see above comments).
 	 */
-	btrfs_clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start, end,
+	btrfs_clear_extent_bit(io_tree, page_start, end,
 			       EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
 			       EXTENT_DEFRAG, &cached_state);