mmc: mediatek: set b_max according CONFIG_SYS_MMC_MAX_BLK_COUNT

The block count limit on MMC based devices should be set according to
CONFIG_SYS_MMC_MAX_BLK_COUNT instead of hardcoding value.

Signed-off-by: Julien Masson <jmasson@baylibre.com>
diff --git a/drivers/mmc/mtk-sd.c b/drivers/mmc/mtk-sd.c
index d21a30c..5a0c61d 100644
--- a/drivers/mmc/mtk-sd.c
+++ b/drivers/mmc/mtk-sd.c
@@ -1665,7 +1665,7 @@
 	if (cfg->f_max < cfg->f_min || cfg->f_max > host->src_clk_freq)
 		cfg->f_max = host->src_clk_freq;
 
-	cfg->b_max = 1024;
+	cfg->b_max = CONFIG_SYS_MMC_MAX_BLK_COUNT;
 	cfg->voltages = MMC_VDD_32_33 | MMC_VDD_33_34;
 
 	host->mmc = &plat->mmc;