mips/malta: fix board id

Board id can't be written with stl_phys() as it's read-only part of
memory. Use stl_p() on the memory buffer instead.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

hw/mips_malta.c

@@ -910,7 +910,7 @@ void mips_malta_init (ram_addr_t ram_size,
     /* Board ID = 0x420 (Malta Board with CoreLV)
        XXX: theoretically 0x1e000010 should map to flash and 0x1fc00010 should
        map to the board ID. */
-    stl_phys(0x1fc00010LL, 0x00000420);
+    stl_p(qemu_get_ram_ptr(bios_offset) + 0x10, 0x00000420);
 
     /* Init internal devices */
     cpu_mips_irq_init_cpu(env);