ARM: dts: imx53-qsb: SDHC3 is connected in 8-bit mode

SDHC3 is 8 bit-wide, so pass the bus-width property to reflect that.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>