hw/scsi/megasas: Use uint32_t for reply queue head/tail values

While the reply queue values fit in 16-bit, they are accessed
as 32-bit:

  661:    s->reply_queue_head = ldl_le_pci_dma(pcid, s->producer_pa);
  662:    s->reply_queue_head %= MEGASAS_MAX_FRAMES;
  663:    s->reply_queue_tail = ldl_le_pci_dma(pcid, s->consumer_pa);
  664:    s->reply_queue_tail %= MEGASAS_MAX_FRAMES;

Having:

  41:#define MEGASAS_MAX_FRAMES 2048         /* Firmware limit at 65535 */

In order to update the ld/st*_pci_dma() API to pass the address
of the value to access, it is simpler to have the head/tail declared
as 32-bit values. Replace the uint16_t by uint32_t, wasting 4 bytes in
the MegasasState structure.

Acked-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211223115554.3155328-20-philmd@redhat.com>