mxc: Fix SDHC multi-instance clock

On mxc, each SDHC instance has a dedicated clock, so gd->sdhc_clk is not
suitable for the multi-instance use case (initialization made directly with
fsl_esdhc_initialize()).

This patch fixes this issue by adding a configuration field for the SDHC input
clock frequency.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Eric Bénard <eric@eukrea.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Jason Liu <r64343@freescale.com>
Cc: Matt Sealey <matt@genesi-usa.com>
Cc: Andy Fleming <afleming@gmail.com>
diff --git a/board/freescale/mx6qsabrelite/mx6qsabrelite.c b/board/freescale/mx6qsabrelite/mx6qsabrelite.c
index 4b4e89b..3af8437 100644
--- a/board/freescale/mx6qsabrelite/mx6qsabrelite.c
+++ b/board/freescale/mx6qsabrelite/mx6qsabrelite.c
@@ -264,6 +264,9 @@
        s32 status = 0;
        u32 index = 0;
 
+	usdhc_cfg[0].sdhc_clk = mxc_get_clock(MXC_ESDHC3_CLK);
+	usdhc_cfg[1].sdhc_clk = mxc_get_clock(MXC_ESDHC4_CLK);
+
        for (index = 0; index < CONFIG_SYS_FSL_USDHC_NUM; ++index) {
 	       switch (index) {
 	       case 0: