pinctrl: just return if no valid maps

If there is a problem with a pinctrl node of a device,
for example, config child node do not have prop specified in
dt_params, num_maps maybe 0. On this condition, no need remember
this map.

Signed-off-by: lijiazi <lijiazi@xiaomi.com>
Link: https://lore.kernel.org/r/29421e7720443a2454830963186f00583c76ce1e.1572588550.git.lijiazi@xiaomi.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>