use PACKED macro insted of open-coding GCC-ism

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/volume_id/reiserfs.c b/util-linux/volume_id/reiserfs.c
index b8cdc98..1298f86 100644
--- a/util-linux/volume_id/reiserfs.c
+++ b/util-linux/volume_id/reiserfs.c
@@ -35,7 +35,7 @@
 	uint32_t	dummy4[5];
 	uint8_t		uuid[16];
 	uint8_t		label[16];
-} __attribute__((__packed__));
+} PACKED;
 
 struct reiser4_super_block {
 	uint8_t		magic[16];
@@ -43,7 +43,7 @@
 	uint8_t		uuid[16];
 	uint8_t		label[16];
 	uint64_t	dummy2;
-} __attribute__((__packed__));
+} PACKED;
 
 #define REISERFS1_SUPERBLOCK_OFFSET		0x2000
 #define REISERFS_SUPERBLOCK_OFFSET		0x10000