btrfs: remove unused parameter nr_pages in add_ra_bio_pages()

Variable @nr_pages only gets increased but never used.  Remove it.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -551,7 +551,6 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 	u64 isize = i_size_read(inode);
 	int ret;
 	struct page *page;
-	unsigned long nr_pages = 0;
 	struct extent_map *em;
 	struct address_space *mapping = inode->i_mapping;
 	struct extent_map_tree *em_tree;
@@ -647,7 +646,6 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 				   PAGE_SIZE, 0);
 
 		if (ret == PAGE_SIZE) {
-			nr_pages++;
 			put_page(page);
 		} else {
 			unlock_extent(tree, last_offset, end);