[JFFS2] Repack some on-medium structures. ARM is weirder than I thought.

We have to pack at least the jint16_t structure, because otherwise it'll
be four bytes in size. Thankfully, we can do that and _not_ pack the
actual node structures, and the compiler still doesn't emit stupid code.
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/jffs2.h

@@ -82,15 +82,15 @@
 
 typedef struct {
 	uint32_t v32;
-} jint32_t;
+} __attribute__((packed)) jint32_t;
 
 typedef struct {
 	uint32_t m;
-} jmode_t;
+} __attribute__((packed)) jmode_t;
 
 typedef struct {
 	uint16_t v16;
-} jint16_t;
+} __attribute__((packed)) jint16_t;
 
 struct jffs2_unknown_node
 {