netfilter: nf_nat_snmp_basic: add correct dependency to Makefile

nf_nat_snmp_basic_main.c includes a generated header, but the
necessary dependency is missing in Makefile. This could cause
build error in parallel building.

Remove a weird line, and add a correct one.

Fixes: cc2d5863 ("netfilter: nf_nat_snmp_basic: use asn1 decoder library")
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

net/ipv4/netfilter/Makefile

@@ -29,7 +29,7 @@ obj-$(CONFIG_NF_NAT_H323) += nf_nat_h323.o
 obj-$(CONFIG_NF_NAT_PPTP) += nf_nat_pptp.o
 
 nf_nat_snmp_basic-y := nf_nat_snmp_basic-asn1.o nf_nat_snmp_basic_main.o
-nf_nat_snmp_basic-y : nf_nat_snmp_basic-asn1.h nf_nat_snmp_basic-asn1.c
+$(obj)/nf_nat_snmp_basic_main.o: $(obj)/nf_nat_snmp_basic-asn1.h
 obj-$(CONFIG_NF_NAT_SNMP_BASIC) += nf_nat_snmp_basic.o
 clean-files := nf_nat_snmp_basic-asn1.c nf_nat_snmp_basic-asn1.h