mmc: mtk-sd: assign plat->cfg.f_max with a correct value

Currently this driver does not set the value of plat->cfg.f_max, which
results in that MMC framework will always run at the lowest frequency.

This patch sets plat->cfg.f_max to the maximum allowed frequency, which
equals to the source clock frequency.

Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

drivers/mmc/mtk-sd.c

@@ -1639,6 +1639,8 @@ static int msdc_drv_probe(struct udevice *dev)
 	else
 		cfg->f_min = host->src_clk_freq / (4 * 4095);
 
+	cfg->f_max = host->src_clk_freq;
+
 	cfg->b_max = 1024;
 	cfg->voltages = MMC_VDD_32_33 | MMC_VDD_33_34;