Fixed missed use of INSTALL_TOP

Thanks to sylr@github
Signed-off-by: NPedro Melo <melo@simplicidade.org>

src/Makefile

@@ -16,7 +16,7 @@ CCOPT= $(CFLAGS) $(CCLINK) $(ARCH) $(PROF)
 DEBUG?= -g -rdynamic -ggdb 
 
 PREFIX= /usr/local
-INSTALL_BIN= $(INSTALL_TOP)/bin
+INSTALL_BIN= $(PREFIX)/bin
 INSTALL= cp -p
 
 OBJ = adlist.o ae.o anet.o dict.o redis.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking.o util.o object.o db.o replication.o rdb.o t_string.o t_list.o t_set.o t_zset.o t_hash.o config.o aof.o vm.o pubsub.o multi.o debug.o sort.o intset.o