VXLAN: Fix sparse warnings.

Fixes following warning:-
drivers/net/vxlan.c:471:35: warning: symbol 'dev' shadows an earlier one
drivers/net/vxlan.c:433:26: originally declared here
drivers/net/vxlan.c:794:34: warning: symbol 'vxlan' shadows an earlier one
drivers/net/vxlan.c:757:26: originally declared here

CC: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>