omni: make soong variables follow json syntax

wrong: CROSS_COMPILE=\\"/data4...
correct: CROSS_COMPILE=\"/data4...

Change-Id: I5080aef7feb2ec7429cb9ba1f4baccefa61a3cd3
diff --git a/config/BoardConfigSoong.mk b/config/BoardConfigSoong.mk
index cff1700..9ca2268 100644
--- a/config/BoardConfigSoong.mk
+++ b/config/BoardConfigSoong.mk
@@ -18,7 +18,7 @@
 
 define addVar
   SOONG_CONFIG_omniromVarsPlugin += $(1)
-  SOONG_CONFIG_omniromVarsPlugin_$(1) := $$(subst ",\",$$($1))
+  SOONG_CONFIG_omniromVarsPlugin_$(1) := $($1)
 endef
 
 $(foreach v,$(EXPORT_TO_SOONG),$(eval $(call addVar,$(v))))