MLK-12563: imx: mx6ul evk: fix LCD_nPWREN setting

Q901 is PMOS, LCD_nPWREN should be at low voltage then output is 3V3.
If LCD_nPWREN is high, output is 2.4V which is not correct.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
(cherry picked from commit b54bb711)