CorebootModulePkg: Reformat asm constant to avoid gcc assembler fail

The gnu assembler doesn't allow multiple '$' in an expression.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Scott Duplichan <scott@notabs.org>
---

Index: CorebootModulePkg/SecCore/Ia32/SecEntry.S
===================================================================
--- CorebootModulePkg/SecCore/Ia32/SecEntry.S	(revision 17108)
+++ CorebootModulePkg/SecCore/Ia32/SecEntry.S	(working copy)
@@ -46,7 +46,7 @@
   #
   # Construct the temporary memory at 0x80000, length 0x10000
   #
-  movl ($BASE_512KB + $SIZE_64KB), %esp
+  movl $(BASE_512KB + SIZE_64KB), %esp
 
   #
   # Pass BFV into the PEI Core