ARM: dts: imx6qdl-sabresd: remove reg_sensors' regulator-always-on

Now that all sensors supplied by reg_sensors have supported
regulator control, reg_sensors does NOT need to be always ON,
remove "regulator-always-on" to save power.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>