mb/*/*: Clean up FADT checksum assignment

The assignment of header->checksum was in some cases done twice, or
unnecessarily split into two lines.

Change-Id: Ib0c0890d7589e6a24b11e9bda10e6969c7d73c56
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/28988
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>

src/mainboard/intel/camelbackmountain_fsp/fadt.c

@@ -23,7 +23,5 @@ void acpi_create_fadt(acpi_fadt_t *fadt, acpi_facs_t *facs, void *dsdt)
 
 	/* Platform specific customizations go here */
 
-	header->checksum = 0;
-	header->checksum =
-		acpi_checksum((void *) fadt, sizeof(acpi_fadt_t));
+	header->checksum = acpi_checksum((void *) fadt, sizeof(acpi_fadt_t));
 }