aspeed/smc: Remove the 'size' attribute from AspeedSMCFlash

AspeedSMCFlash::size is only used to compute the initial size of the
boot_rom region. Not very useful, so directly call memory_region_size()
instead.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

include/hw/ssi/aspeed_smc.h

@@ -34,7 +34,6 @@ typedef struct AspeedSMCFlash {
     struct AspeedSMCState *controller;
 
     uint8_t id;
-    uint32_t size;
 
     MemoryRegion mmio;
 } AspeedSMCFlash;