[Ameba] Fix Trailing Null (#22836)

* TC-BINFO-2.1 when reading location, it shows 3 chars. Remove trailing null after getPref_str_new
diff --git a/src/platform/Ameba/AmebaConfig.cpp b/src/platform/Ameba/AmebaConfig.cpp
index 5c22877..cd03445 100644
--- a/src/platform/Ameba/AmebaConfig.cpp
+++ b/src/platform/Ameba/AmebaConfig.cpp
@@ -152,6 +152,7 @@
 
     if (success == 0)
     {
+        outLen -= 1; // Don't count trailing null
         return CHIP_NO_ERROR;
     }
     else