hw/adc/stm32f2xx_adc: Correct memory region size and access size

The ADC region size is 256B, split as:
 - [0x00 - 0x4f] defined
 - [0x50 - 0xff] reserved

All registers are 32-bit (thus when the datasheet mentions the
last defined register is 0x4c, it means its address range is
0x4c .. 0x4f.

This model implementation is also 32-bit. Set MemoryRegionOps
'impl' fields.

See:
  'RM0033 Reference manual Rev 8', Table 10.13.18 "ADC register map".

Reported-by: Seth Kintigh <skintigh@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20200603055915.17678-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/adc/stm32f2xx_adc.c

@@ -246,6 +246,8 @@ static const MemoryRegionOps stm32f2xx_adc_ops = {
     .read = stm32f2xx_adc_read,
     .write = stm32f2xx_adc_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
+    .impl.min_access_size = 4,
+    .impl.max_access_size = 4,
 };
 
 static const VMStateDescription vmstate_stm32f2xx_adc = {
@@ -278,7 +280,7 @@ static void stm32f2xx_adc_init(Object *obj)
     sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->irq);
 
     memory_region_init_io(&s->mmio, obj, &stm32f2xx_adc_ops, s,
-                          TYPE_STM32F2XX_ADC, 0xFF);
+                          TYPE_STM32F2XX_ADC, 0x100);
     sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->mmio);
 }