mmc: mediatek: add HS400 support

Hello Chaotian Jing,

The patch 6397b7f5f405: "mmc: mediatek: add HS400 support" from Oct 27, 2015, leads to the following static checker warning:

	drivers/mmc/host/mtk-sd.c:1320 msdc_tune_response()
	error: uninitialized variable 'cmd_err'.

drivers/mmc/host/mtk-sd.c
1306 static int msdc_tune_response(struct mmc_host *mmc, u32 opcode) 1307 {

  1308          struct msdc_host *host = mmc_priv(mmc);
  1309          u32 rise_delay = 0, fall_delay = 0;
  1310          struct msdc_delay_phase final_rise_delay, final_fall_delay;
  1311          u8 final_delay, final_maxlen;
  1312          int cmd_err;
                    ^^^^^^^
  1313          int i;
  1314  
  1315          sdr_clr_bits(host->base + MSDC_IOCON, MSDC_IOCON_RSPL);
  1316          for (i = 0 ; i < PAD_DELAY_MAX; i++) {
  1317                  sdr_set_field(host->base + MSDC_PAD_TUNE,
  1318                                MSDC_PAD_TUNE_CMDRDLY, i);
  1319                  mmc_send_tuning(mmc, opcode, &cmd_err);
                                                      ^^^^^^^

No error handling.

  1320                  if (!cmd_err)
                             ^^^^^^^
  1321                          rise_delay |= (1 << i);
  1322          }

regards,
dan carpenter