Arm backend: Fix memory mode for Ethos-U85 (#7416)

This fix a minor typo that made run.sh not work for Ethos-U85 if no
--memory_mode was specified.


Signed-off-by: Zingo Andersen <[email protected]>

Author: zingo

examples/arm/run.sh

@@ -114,7 +114,7 @@ then
     memory_mode="Shared_Sram"
     if [[ ${target} =~ "ethos-u85" ]]
     then
-        system_config="Sram_Only"
+        memory_mode="Sram_Only"
     fi
 fi