btrfs: remove redundant variable in __do_readpage

The value of page_end is only stored to end, no other use.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -2886,8 +2886,7 @@ static int __do_readpage(struct extent_io_tree *tree,
 {
 	struct inode *inode = page->mapping->host;
 	u64 start = page_offset(page);
-	u64 page_end = start + PAGE_SIZE - 1;
-	u64 end;
+	const u64 end = start + PAGE_SIZE - 1;
 	u64 cur = start;
 	u64 extent_offset;
 	u64 last_byte = i_size_read(inode);
@@ -2905,7 +2904,6 @@ static int __do_readpage(struct extent_io_tree *tree,
 
 	set_page_extent_mapped(page);
 
-	end = page_end;
 	if (!PageUptodate(page)) {
 		if (cleancache_get_page(page) == 0) {
 			BUG_ON(blocksize != PAGE_SIZE);