jffs2: Fix long-standing bug with symlink garbage collection.

Ever since jffs2_garbage_collect_metadata() was first half-written in
February 2001, it's been broken on architectures where 'char' is signed.
When garbage collecting a symlink with target length above 127, the payload
length would end up negative, causing interesting and bad things to happen.

Cc: stable@kernel.org
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

fs/jffs2/gc.c

@@ -700,7 +700,8 @@ static int jffs2_garbage_collect_metadata(struct jffs2_sb_info *c, struct jffs2_
 	struct jffs2_raw_inode ri;
 	struct jffs2_node_frag *last_frag;
 	union jffs2_device_node dev;
-	char *mdata = NULL, mdatalen = 0;
+	char *mdata = NULL;
+	int mdatalen = 0;
 	uint32_t alloclen, ilen;
 	int ret;