CorebootPayloadPkg: Fix GCC build issue on macro definition

CorebootPayloadPkg: Fix GCC build issue on macro definition

The previous change to disable deprecated APIs in CorebootPayloadPkg
used "/D" instead of "-D".  It caused Linux GCC build error. Correct
it to use "-D" instead.

Cc: Prince Agyeman <prince.agyeman@intel.com>
Cc: Rusty Coleman <rcoleman@sigovs.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Prince Agyeman <prince.agyeman@intel.com>
Reviewed-by: Rusty Coleman <rcoleman@sigovs.com>