coverage is misspelled as coverate

[YzhDDDing]

Hello, I found that in makefile coverage is misspelled as coverate, so the coverage option is not passed to Verilator, disabling coverage-related instrumentation and mutation behavior.

$(SUBDIRS):
	@$(MAKE) $(MAKE_FLAGS) memsize=$(memsize) -C sw $@
	@$(MAKE) $(if $(_verilator), verilator=1) \
			 $(if $(_coverage), **coverate**=1) \
			 $(if $(_top), top=1) $(MAKE_FLAGS) memsize=$(memsize) debug=$(debug) -C sim $@.elf
	@$(MAKE) $(if $(_top), top=1) $(MAKE_FLAGS) memsize=$(memsize) tracelog=1 -C tools $@.elf
	@echo "Compare the trace between RTL and ISS simulator"
	@diff --brief sim/trace.log tools/trace.log
	@echo === Simulation passed ===