mpls_iptunnel: fix sparse warn: remove incorrect rcu_dereference

fix for:
net/mpls/mpls_iptunnel.c:73:19: sparse: incompatible types in comparison
expression (different address spaces)

remove incorrect rcu_dereference possibly left over from
earlier revisions of the code.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>