hw/i2c/pm_smbus: Remove dead assignment

Fix warning reported by Clang static code analyzer:

    CC      hw/i2c/pm_smbus.o
  hw/i2c/pm_smbus.c:187:17: warning: Value stored to 'ret' is never read
                  ret = 0;
                  ^     ~

Reported-by: Clang Static Analyzer
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200422133152.16770-4-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/i2c/pm_smbus.c

@@ -184,7 +184,6 @@ static void smb_transaction(PMSMBus *s)
                 s->smb_stat |= STS_HOST_BUSY | STS_BYTE_DONE;
                 s->smb_data[0] = s->smb_blkdata;
                 s->smb_index = 0;
-                ret = 0;
             }
             goto out;
         }