Silicon/Socionext: fix unused variable error NorFlashFvb

When building in NOOPT mode, SynQuacer/Drivers/Fip006Dxe/NorFlashFvb.c
fails to build with -Werror=unused-but-set-variable due to the Instance
variable being set from the This pointer but never actually referenced.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>