Fix variable name in run_test.sh

Top of the file declares KVM_MODE but code uses just MODE. Fix this.
Problem only manifests itself if run_test.sh is invoked without -M.
In that case, MODE is undefined when referenced for the first time.

Test: ./build/kvm-unit-tests/run_test.sh psci
Change-Id: I2c042f1aa73da33ebb1a333bc79f9383f27dde82
diff --git a/kvm-unit-tests/run_test.sh b/kvm-unit-tests/run_test.sh
index a0c6228..afd7c4b 100755
--- a/kvm-unit-tests/run_test.sh
+++ b/kvm-unit-tests/run_test.sh
@@ -20,7 +20,7 @@
 default_var VERBOSE		0
 default_var QUIET		0
 default_var GDB			0
-default_var KVM_MODE		""
+default_var MODE		""
 default_var KERNEL		""
 default_var FIRMWARE		""
 default_var TEST_PATH		""