desc->flags may already have values set by of_gpiochip_add() so make
sure that this isn't undone when setting the initial direction.

Cc: stable@vger.kernel.org
Fixes: 3edfb7bd ("gpiolib: Show correct direction from the beginning")
Signed-off-by: NChris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20190707203558.10993-1-chris.packham@alliedtelesis.co.nzSigned-off-by: NLinus Walleij <linus.walleij@linaro.org>