mmc: sdhci-of-at91: fix CALCR register being rewritten

When enabling calibration at reset, the CALCR register was completely
rewritten. This may cause certain bits being deleted unintentedly.
Fix by issuing a read-modify-write operation.

Fixes: 727d836a375a ("mmc: sdhci-of-at91: add DT property to enable calibration on full reset")
Signed-off-by: Eugen Hristev <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Cc: [e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/sdhci-of-at91.c

···
 	    || mmc_gpio_get_cd(host->mmc) >= 0)
 		sdhci_at91_set_force_card_detect(host);
 
-	if (priv->cal_always_on && (mask & SDHCI_RESET_ALL))
-		sdhci_writel(host, SDMMC_CALCR_ALWYSON | SDMMC_CALCR_EN,
+	if (priv->cal_always_on && (mask & SDHCI_RESET_ALL)) {
+		u32 calcr = sdhci_readl(host, SDMMC_CALCR);
+
+		sdhci_writel(host, calcr | SDMMC_CALCR_ALWYSON | SDMMC_CALCR_EN,
 			     SDMMC_CALCR);
+	}
 }
 
 static const struct sdhci_ops sdhci_at91_sama5d2_ops = {