Fix typo in Makefile (#2154)

Signed-off-by: jorturfer <[email protected]>

Makefile

@@ -225,7 +225,7 @@ envtest: ## Download envtest-setup locally if necessary.
 
 MOCKGEN = $(shell pwd)/bin/mockgen
 mockgen: ## Download mockgen locally if necessary.
-	$(call go-get-tool,$(ENVTEST),github.com/golang/mock/[email protected])
+	$(call go-get-tool,$(MOCKGEN),github.com/golang/mock/[email protected])
 
 # go-get-tool will 'go get' any package $2 and install it to $1.
 PROJECT_DIR := $(shell dirname $(abspath $(lastword $(MAKEFILE_LIST))))