lib/Makefile: Fix oid_registry build dependency

It is $(obj)/oid_registry.o that is dependent on $(obj)/oid_registry_data.c.
The object file cannot be built until $(obj)/oid_registry_data.c has been
generated.

A periodic and hard to reproduce parallel build failure is due to
this incorrect lib/Makefile dependency. The compile error is completely
disingenuous.

  GEN     lib/oid_registry_data.c
Compiling 49 OIDs
  CC      lib/oid_registry.o
gcc: error: lib/oid_registry.c: No such file or directory
gcc: fatal error: no input files
compilation terminated.
make[3]: *** [lib/oid_registry.o] Error 4

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lib/Makefile

@@ -163,7 +163,7 @@ $(obj)/crc32table.h: $(obj)/gen_crc32table
 #
 obj-$(CONFIG_OID_REGISTRY) += oid_registry.o
 
-$(obj)/oid_registry.c: $(obj)/oid_registry_data.c
+$(obj)/oid_registry.o: $(obj)/oid_registry_data.c
 
 $(obj)/oid_registry_data.c: $(srctree)/include/linux/oid_registry.h \
 			    $(src)/build_OID_registry