Fix typo in MODULE_BUILD_FROM_SOURCE variable.

Cherry-picked from http://ag/15300830.

Test: env MODULE_BUILD_FROM_SOURCE=true \
        TARGET_PRODUCT=cf_x86_64_phone build/soong/soong_ui.bash \
        --dumpvar-mode SOONG_CONFIG_art_module_source_build
  returns true
Test: env TARGET_PRODUCT=cf_x86_64_phone build/soong/soong_ui.bash \
        --dumpvar-mode SOONG_CONFIG_art_module_source_build
  returns false
Bug: 191978129
Change-Id: I2056b198bc0b944a6736ff21077b902df13c1479
Merged-In: I2056b198bc0b944a6736ff21077b902df13c1479
diff --git a/core/android_soong_config_vars.mk b/core/android_soong_config_vars.mk
index 46b588e..7cd8489 100644
--- a/core/android_soong_config_vars.mk
+++ b/core/android_soong_config_vars.mk
@@ -43,7 +43,7 @@
   # Always build from source for the module targets. This ought to be covered by
   # the TARGET_BUILD_APPS check above, but there are test builds that don't set it.
   SOONG_CONFIG_art_module_source_build := true
-else ifdef MODULES_BUILD_FROM_SOURCE
+else ifdef MODULE_BUILD_FROM_SOURCE
   # Build from source if other Mainline modules are.
   SOONG_CONFIG_art_module_source_build := true
 else ifneq (,$(filter true,$(NATIVE_COVERAGE) $(CLANG_COVERAGE)))