md-bitmap: initialize variables at declaration time in md_bitmap_file_unmap

Just a small tidyup to prepare for bigger changes.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230615064840.629492-3-hch@lst.de

drivers/md/md-bitmap.c

@@ -842,14 +842,10 @@ static int md_bitmap_storage_alloc(struct bitmap_storage *store,
 
 static void md_bitmap_file_unmap(struct bitmap_storage *store)
 {
-	struct page **map, *sb_page;
-	int pages;
-	struct file *file;
-
-	file = store->file;
-	map = store->filemap;
-	pages = store->file_pages;
-	sb_page = store->sb_page;
+	struct file *file = store->file;
+	struct page *sb_page = store->sb_page;
+	struct page **map = store->filemap;
+	int pages = store->file_pages;
 
 	while (pages--)
 		if (map[pages] != sb_page) /* 0 is sb_page, release it below */