erofs: fix 'backmost' member of z_erofs_decompress_frontend

Initialize 'backmost' to true in DECOMPRESS_FRONTEND_INIT.

Fixes: 5c6dcc57 ("erofs: get rid of `struct z_erofs_collector'")
Signed-off-by: Weizhao Ouyang <o451686892@gmail.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20220530075114.918874-1-o451686892@gmail.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/zdata.c

@@ -213,7 +213,7 @@ struct z_erofs_decompress_frontend {
 
 #define DECOMPRESS_FRONTEND_INIT(__i) { \
 	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
-	.mode = COLLECT_PRIMARY_FOLLOWED }
+	.mode = COLLECT_PRIMARY_FOLLOWED, .backmost = true }
 
 static struct page *z_pagemap_global[Z_EROFS_VMAP_GLOBAL_PAGES];
 static DEFINE_MUTEX(z_pagemap_global_lock);