vxlan: remove unused variable saddr in neigh_reduce

silences the below warning:
    drivers/net/vxlan.c: In function ‘neigh_reduce’:
    drivers/net/vxlan.c:1599:25: warning: variable ‘saddr’ set but not used
    [-Wunused-but-set-variable]

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>