mmc: moxart: fix 4-bit bus width and remove 8-bit bus width

According to the datasheet [1] at page 377, 4-bit bus width is turned on by
bit 2 of the Bus Width Register. Thus the current bitmask is wrong: define
BUS_WIDTH_4 BIT(1)

BIT(1) does not work but BIT(2) works. This has been verified on real MOXA
hardware with FTSDC010 controller revision 1_6_0.

The corrected value of BUS_WIDTH_4 mask collides with: define BUS_WIDTH_8
BIT(2). Additionally, 8-bit bus width mode isn't supported according to the
datasheet, so let's remove the corresponding code.

[1]
https://bitbucket.org/Kasreyn/mkrom-uc7112lx/src/master/documents/FIC8120_DS_v1.2.pdf

Fixes: 1b66e94 ("mmc: moxart: Add MOXA ART SD/MMC driver")
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220907205753.1577434-1-saproj@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/moxart-mmc.c

@@ -111,8 +111,8 @@
 #define CLK_DIV_MASK		0x7f
 
 /* REG_BUS_WIDTH */
-#define BUS_WIDTH_8		BIT(2)
-#define BUS_WIDTH_4		BIT(1)
+#define BUS_WIDTH_4_SUPPORT	BIT(3)
+#define BUS_WIDTH_4		BIT(2)
 #define BUS_WIDTH_1		BIT(0)
 
 #define MMC_VDD_360		23
@@ -524,9 +524,6 @@ static void moxart_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 	case MMC_BUS_WIDTH_4:
 		writel(BUS_WIDTH_4, host->base + REG_BUS_WIDTH);
 		break;
-	case MMC_BUS_WIDTH_8:
-		writel(BUS_WIDTH_8, host->base + REG_BUS_WIDTH);
-		break;
 	default:
 		writel(BUS_WIDTH_1, host->base + REG_BUS_WIDTH);
 		break;
@@ -651,16 +648,8 @@ static int moxart_probe(struct platform_device *pdev)
 		dmaengine_slave_config(host->dma_chan_rx, &cfg);
 	}
 
-	switch ((readl(host->base + REG_BUS_WIDTH) >> 3) & 3) {
-	case 1:
+	if (readl(host->base + REG_BUS_WIDTH) & BUS_WIDTH_4_SUPPORT)
 		mmc->caps |= MMC_CAP_4_BIT_DATA;
-		break;
-	case 2:
-		mmc->caps |= MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA;
-		break;
-	default:
-		break;
-	}
 
 	writel(0, host->base + REG_INTERRUPT_MASK);