chore: fix backfill-redis Makefile target (#1685)

This commit makes a minor change to the Makefile's `backfill-redis`
target to output a binary named `backfill-redis`, fixing what was
probably a simple copy/paste error when the target was introduced.

Signed-off-by: Lance Ball <lball@redhat.com>

Makefile

@@ -83,7 +83,7 @@ rekor-server: $(SRCS)
 	CGO_ENABLED=0 go build -trimpath -ldflags "$(SERVER_LDFLAGS)" -o rekor-server ./cmd/rekor-server
 
 backfill-redis: $(SRCS)
-	CGO_ENABLED=0 go build -trimpath -ldflags "$(SERVER_LDFLAGS)" -o rekor-server ./cmd/backfill-redis
+	CGO_ENABLED=0 go build -trimpath -ldflags "$(SERVER_LDFLAGS)" -o backfill-redis ./cmd/backfill-redis
 
 test:
 	go test ./...