Makefile: fix old make check thinko

So it doesn't fail with 3.81.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -28,7 +28,7 @@ export BR2_VERSION:=2012.02-git
 
 # Check for minimal make version (note: this check will break at make 10.x)
 MIN_MAKE_VERSION=3.81
-ifeq ($(firstword $(sort $(MAKE_VERSION) $(MIN_MAKE_VERSION))),$(MAKE_VERSION))
+ifneq ($(firstword $(sort $(MAKE_VERSION) $(MIN_MAKE_VERSION))),$(MIN_MAKE_VERSION))
 $(error You have make '$(MAKE_VERSION)' installed. GNU make >= $(MIN_MAKE_VERSION) is required)
 endif