leds: lp55xx: Initialize enable GPIO direction to output

The "Convert to use GPIO descriptors" commit changed the
initialization of the enable GPIO from GPIOF_DIR_OUT to
GPIOD_ASIS.  This breaks systems where the GPIO does not
default to output.  Changing the enable initialization
to GPIOD_OUT_LOW.

Signed-off-by: Doug Zobel <dougdev334@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>