hw/rx/rx-gdbsim: Remove unnecessary uses of &first_cpu

rx_gdbsim_init() has access to the single CPU via:

  RxGdbSimMachineState {
    RX62NState {
      RXCPU cpu;
      ...
    } mcu;
  } s;

Directly use that instead of the &first_cpu global.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250110180442.82687-1-philmd@linaro.org>

hw/rx/rx-gdbsim.c

@@ -127,7 +127,7 @@ static void rx_gdbsim_init(MachineState *machine)
          * the latter half of the SDRAM space.
          */
         kernel_offset = machine->ram_size / 2;
-        rx_load_image(RX_CPU(first_cpu), kernel_filename,
+        rx_load_image(&s->mcu.cpu, kernel_filename,
                       SDRAM_BASE + kernel_offset, kernel_offset);
         if (dtb_filename) {
             ram_addr_t dtb_offset;
@@ -153,7 +153,7 @@ static void rx_gdbsim_init(MachineState *machine)
             qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
                                 rom_ptr(SDRAM_BASE + dtb_offset, dtb_size));
             /* Set dtb address to R1 */
-            RX_CPU(first_cpu)->env.regs[1] = SDRAM_BASE + dtb_offset;
+            s->mcu.cpu.env.regs[1] = SDRAM_BASE + dtb_offset;
         }
     }
 }