arm/mxs: fix mmc device adding for mach-mx28evk

The merge commit "526b2641 Merge branch 'imx/cleanup' into imx/devel"
left a duplicated mx28_add_mxs_mmc() call, which causes the problem
below during boot.

  kobject_add_internal failed for mxs-mmc.1 with -EEXIST, don't try
  to register things with the same name in the same directory.

The patch removes this leftover and also change mmc0 adding to align
with mmc1.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-mxs/mach-mx28evk.c

@@ -471,7 +471,8 @@ static void __init mx28evk_init(void)
 			       "mmc0-slot-power");
 	if (ret)
 		pr_warn("failed to request gpio mmc0-slot-power: %d\n", ret);
-	mx28_add_mxs_mmc(0, &mx28evk_mmc_pdata[0]);
+	else
+		mx28_add_mxs_mmc(0, &mx28evk_mmc_pdata[0]);
 
 	ret = gpio_request_one(MX28EVK_MMC1_SLOT_POWER, GPIOF_OUT_INIT_LOW,
 			       "mmc1-slot-power");
@@ -480,7 +481,6 @@ static void __init mx28evk_init(void)
 	else
 		mx28_add_mxs_mmc(1, &mx28evk_mmc_pdata[1]);
 
-	mx28_add_mxs_mmc(1, &mx28evk_mmc_pdata[1]);
 	mx28_add_rtc_stmp3xxx();
 
 	gpio_led_register_device(0, &mx28evk_led_data);