net: ping: cleanups ping_v4_unhash()

net/ipv4/ping.c: In function ‘ping_v4_unhash’:
net/ipv4/ping.c:140:28: warning: variable ‘hslot’ set but not used

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: David S. Miller <davem@davemloft.net>