thunderbolt: Remove redundant assignment to variable len

The variable len is assigned a value that is never read. It is re-assigned
a new value in the following do-while loop and never referenced after
the loop. The assignment is redundant and can be removed.

Cleans up clang scan build warning:
drivers/thunderbolt/xdomain.c:344:2: warning: Value stored to 'len' is
never read [deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/xdomain.c

@@ -342,7 +342,6 @@ static int tb_xdp_properties_request(struct tb_ctl *ctl, u64 route,
 	memcpy(&req.src_uuid, src_uuid, sizeof(*src_uuid));
 	memcpy(&req.dst_uuid, dst_uuid, sizeof(*dst_uuid));
 
-	len = 0;
 	data_len = 0;
 
 	do {