small decrease in nangate45/swerv utilization to avoid grt congestion

Signed-off-by: Augusto Berndt <augusto.berndt@precisioninno.com>

Author: gudeh

flow/designs/nangate45/swerv/config.mk

@@ -4,7 +4,7 @@ export PLATFORM    = nangate45
 export VERILOG_FILES = $(DESIGN_HOME)/src/$(DESIGN_NAME)/swerv_wrapper.sv2v.v
 export SDC_FILE      = $(DESIGN_HOME)/$(PLATFORM)/$(DESIGN_NAME)/constraint.sdc
 
-export CORE_UTILIZATION = 65
+export CORE_UTILIZATION = 64
 export CORE_ASPECT_RATIO = 1
 export CORE_MARGIN = 5