net: remove a sparse error in secure_dccpv6_sequence_number()

make C=2 CF=-D__CHECK_ENDIAN__ net/core/secure_seq.o
net/core/secure_seq.c:157:50: warning: restricted __be32 degrades to
integer

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>