x86, efi: Fix 32-bit EFI handover protocol entry point

If the bootloader calls the EFI handover entry point as a standard function
call, then it'll have a return address on the stack. We need to pop that
before calling efi_main(), or the arguments will all be out of position on
the stack.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1358513837.2397.247.camel@shinybook.infradead.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Matt Fleming <matt.fleming@intel.com>

arch/x86/boot/compressed/head_32.S

@@ -50,8 +50,10 @@ ENTRY(startup_32)
 	pushl	%eax
 	pushl	%esi
 	pushl	%ecx
+	sub	$0x4, %esp
 
 	.org 0x30,0x90
+	add	$0x4, %esp
 	call	efi_main
 	cmpl	$0, %eax
 	movl	%eax, %esi