contrib: itmdump: fix multi byte decoding

Incorrect byte manipulations.

Change-Id: Id8c3f457b39f4b2b75613076d403359c4972a69d
Signed-off-by: Karl Palsson <karlp@tweak.net.au>
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2448
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

contrib/itmdump.c

@@ -130,7 +130,7 @@ static bool read_varlen(FILE *f, int c, unsigned *value)
 
 	*value =  (buf[3] << 24)
 		+ (buf[2] << 16)
-		+ (buf[2] << 8)
+		+ (buf[1] << 8)
 		+ (buf[0] << 0);
 	return true;