memory_footprint.py: correct the toolchain name

The toolchain name has been changed from toolchain_GNUARM.cmake to
GCC_7_3_1 on the commit 433771e96f4

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I93b054cd7b0d027282a3e973e47ab0d4fe4f3814
diff --git a/memory_footprint.py b/memory_footprint.py
index 9e12d71..44b193d 100644
--- a/memory_footprint.py
+++ b/memory_footprint.py
@@ -186,7 +186,7 @@
     config = identify_config()
     if (config[2].lower() in REFERENCE_CONFIGS
         and config[0] == "arm/mps2/an521"
-        and config[1] == "toolchain_GNUARM.cmake"):
+        and config[1] == "GCC_7_3_1"):
         # Pushing data for AN521 and GNUARM
         print("Configuration " + config[2] + " is a reference")
         try :