[style] Collapse empty struct bodies to a single line

Adopt the single-line form for empty struct bodies in block.c and
archiver-cpio.c to match the surrounding code style.

Author: jianjunjiang

xstar/driver/block/block.c

@@ -24,8 +24,7 @@
 
 #include <driver/block/block.h>
 
-struct sub_block_pdata_t
-{
+struct sub_block_pdata_t {
 	uint64_t offset;
 	uint64_t length;
 	struct block_t * pblk;

xstar/kernel/xfs/archiver-cpio.c

@@ -49,8 +49,7 @@ struct mhandle_cpio_t {
 	struct block_t * blk;
 };
 
-struct fhandle_cpio_t
-{
+struct fhandle_cpio_t {
 	struct list_head_t head;
 	struct hlist_node_t node;
 	char * name;