Add a comment, no functional change

Describe 2nd byte of the EndTag resource descriptor.

source/components/utilities/utresrc.c

@@ -359,6 +359,13 @@ AcpiUtWalkAmlResources (
                 return_ACPI_STATUS (AE_AML_NO_RESOURCE_END_TAG);
             }
 
+            /*
+             * Don't attempt to perform any validation on the 2nd byte.
+             * Although all known ASL compilers insert a zero for the 2nd
+             * byte, it can also be a checksum (as per the ACPI spec),
+             * and this is occasionally seen in the field. July 2017.
+             */
+
             /* Return the pointer to the EndTag if requested */
 
             if (!UserFunction)