ahci: combine identical clauses in port write

Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180531222835.16558-6-jsnow@redhat.com
Signed-off-by: NJohn Snow <jsnow@redhat.com>

hw/ide/ahci.c

@@ -330,11 +330,7 @@ static void ahci_port_write(AHCIState *s, int port, int offset, uint32_t val)
         check_cmd(s, port);
         break;
     case PORT_TFDATA:
-        /* Read Only. */
-        break;
     case PORT_SIG:
-        /* Read Only */
-        break;
     case PORT_SCR_STAT:
         /* Read Only */
         break;