lsi53c895a: Implement read and write access to DMA Next Address

Fixes the following errors:

lsi_scsi: error: Unhandled writeb 0x28 = 0x0
lsi_scsi: error: Unhandled writeb 0x29 = 0x0
lsi_scsi: error: Unhandled writeb 0x2a = 0x0
lsi_scsi: error: Unhandled writeb 0x2b = 0x0

(cherry picked from commit 4b9a2d6d)

Signed-off-by: Sebastian Herbszt <herbszt@gmx.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/lsi53c895a.c

@@ -1402,6 +1402,7 @@ static uint8_t lsi_reg_readb(LSIState *s, int offset)
     CASE_GET_REG24(dbc, 0x24)
     case 0x27: /* DCMD */
         return s->dcmd;
+    CASE_GET_REG32(dnad, 0x28)
     CASE_GET_REG32(dsp, 0x2c)
     CASE_GET_REG32(dsps, 0x30)
     CASE_GET_REG32(scratch[0], 0x34)
@@ -1594,6 +1595,7 @@ static void lsi_reg_writeb(LSIState *s, int offset, uint8_t val)
         }
         s->ctest5 = val;
         break;
+    CASE_SET_REG32(dnad, 0x28)
     case 0x2c: /* DSP[0:7] */
         s->dsp &= 0xffffff00;
         s->dsp |= val;