ARM: dts: imx6qdl-sabrelite: explicitly set pad for SGTL5000 sys_mclk

Explicitly sets the pad GPIO_0 (sys_mclk) to 0x030b0.

Before this patch, it has the value 0x130b0 if using mainline u-boot.
So this patch also removes hysteresis. The 100k pulldown remains so
that a disabled clock will be low.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>