leds: just ignore invalid GPIOs in leds-gpio

Sometimes it's awkward to make sure that the array in the
platform_data handed to the leds-gpio driver has only valid
data ... some leds may not be always available, and coping
with that currently requires patching or rebuilding the array.

This patch fixes that by making it be OK to pass an invalid
GPIO (such as "-EINVAL") ... such table entries are skipped.

[rpurdie@linux.intel.com: adjusted to apply against other led tree changes]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Tested-by: Diego Dompe <diego.dompe@ridgerun.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>