ppc/amigaone: Constify default_env

The variable holding default env is not supposed to be written.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250314200145.08E0F4E6067@zero.eik.bme.hu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

hw/ppc/amigaone.c

@@ -63,7 +63,7 @@ static const char dummy_fw[] = {
 #define NVRAM_ADDR 0xfd0e0000
 #define NVRAM_SIZE (4 * KiB)
 
-static char default_env[] =
+static const char default_env[] =
     "baudrate=115200\0"
     "stdout=vga\0"
     "stdin=ps2kbd\0"