wrong comment for "Unicode" string.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5842 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/BaseDebugLibSerialPort/DebugLib.c

@@ -112,7 +112,7 @@ DebugAssert (
   CHAR8  Buffer[MAX_DEBUG_MESSAGE_LENGTH];
 
   //
-  // Generate the ASSERT() message in Unicode format
+  // Generate the ASSERT() message in Ascii format
   //
   AsciiSPrint (Buffer, sizeof (Buffer), "ASSERT %a(%d): %a\n", FileName, LineNumber, Description);