mach-exynos: clock: restore calling dead exynos4_get_mmc_clk()

After rework of code by:

commit: d952796 Exynos5: Use clock_get_periph_rate generic API

function get_mmc_clk() always returns -1 for Exynos 4.

This was caused by omitting, that SDHCI driver for Exynos 4,
calls get_mmc_clk(), with mmc device number as argument,
instead of pinmux peripheral id, like DW MMC driver for Exynos 5.

By this commit, the code directly calls a proper function
to get mmc clock for Exynos 4, without checking the peripheral id.

Tested on: Odroid U3/X2, Trats, Trats2, Odroid XU3, Snow (by Simon).

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

arch/arm/mach-exynos/clock.c

@@ -1661,6 +1661,9 @@ unsigned long get_mmc_clk(int dev_index)
 {
 	enum periph_id id;
 
+	if (cpu_is_exynos4())
+		return exynos4_get_mmc_clk(dev_index);
+
 	switch (dev_index) {
 	case 0:
 		id = PERIPH_ID_SDMMC0;
@@ -1679,12 +1682,7 @@ unsigned long get_mmc_clk(int dev_index)
 		return -1;
 	}
 
-	if (cpu_is_exynos5())
-		return clock_get_periph_rate(id);
-	else if (cpu_is_exynos4())
-		return exynos4_get_mmc_clk(dev_index);
-
-	return 0;
+	return clock_get_periph_rate(id);
 }
 
 void set_mmc_clk(int dev_index, unsigned int div)