btrfs: use the same uptodate variable for end_bio_extent_readpage()

In function end_bio_extent_readpage() we call
endio_readpage_release_extent() to unlock the extent io tree.

However we pass PageUptodate(page) as @uptodate parameter for it, while
for previous end_page_read() call, we use a dedicated @uptodate local
variable.

This is not a big deal, as even for subpage cases, either the bio only
covers part of the page, then the @uptodate is always false, and the
subpage ranges can still be merged.

But for the sake of consistency, always use @uptodate variable when
possible.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
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_io.c

@@ -745,7 +745,7 @@ static void end_bio_extent_readpage(struct btrfs_bio *bbio)
 		/* Update page status and unlock. */
 		end_page_read(page, uptodate, start, len);
 		endio_readpage_release_extent(&processed, BTRFS_I(inode),
-					      start, end, PageUptodate(page));
+					      start, end, uptodate);
 
 		ASSERT(bio_offset + len > bio_offset);
 		bio_offset += len;